Category: h2 Database

H2 Database – Truncate ”; Previous Next TRUNCATE is a command used to delete the data from the table. Unlike DELETE FROM without WHERE clause, this command cannot be rolled back. This command commits an open transaction in this connection. Syntax Following is the generic syntax of the truncate command. TRUNCATE TABLE tableName Example In this example, we will truncate a table named test using the following query. TRUNCATE TABLE test; The above query produces the following output. (6) row (s) effected Print Page Previous Next Advertisements ”;

H2 Database – Grant ”; Previous Next Grant is a command coming from the SQL grammar used to grant the rights to a table, to a user, or to a role. Admin rights are required to execute this command. This command commits an open transaction in this connection. In this chapter, we will discuss the different scenarios of Grant command. Grant Right Grant Right is a command to provide admin rights to a table, to a user, or to a role. Syntax Following is the generic syntax of the Grant command. GRANT { SELECT | INSERT | UPDATE | DELETE | ALL } [,…] ON { { SCHEMA schemaName } | { tableName [,…] } } TO { PUBLIC | userName | roleName } Example In this example, we will grant the test table as read-only using the following command. GRANT SELECT ON TEST TO READONLY The above command produces the following output. Grant successfully Grant Alter Any Schema Grant Alter Any Schema is a command to grant schema altering rights to a respective user. Syntax Following is the generic syntax of the Grant Alter Any Schema command. GRANT ALTER ANY SCHEMA TO userName Example In this example, we will grant altering privileges of a schema to a user named test_user. Make sure that test_user exists. Following is the query to grant altering privileges. GRANT ALTER ANY SCHEMA TO test_user; The above query produces the following output. Granted successfully to test_user Print Page Previous Next Advertisements ”;

H2 Database – Create ”; Previous Next CREATE is a generic SQL command used to create Tables, Schemas, Sequences, Views, and Users in H2 Database server. Create Table Create Table is a command used to create a user-defined table in the current database. Syntax Following is the generic syntax for the Create Table command. CREATE [ CACHED | MEMORY ] [ TEMP | [ GLOBAL | LOCAL ] TEMPORARY ] TABLE [ IF NOT EXISTS ] name [ ( { columnDefinition | constraint } [,…] ) ] [ ENGINE tableEngineName [ WITH tableEngineParamName [,…] ] ] [ NOT PERSISTENT ] [ TRANSACTIONAL ] [ AS select ] By using the generic syntax of the Create Table command, we can create different types of tables such as cached tables, memory tables, and temporary tables. Following is the list to describe different clauses from the given syntax. CACHED − The cached tables are the default type for regular tables. This means the number of rows is not limited by the main memory. MEMORY − The memory tables are the default type for temporary tables. This means the memory tables should not get too large and the index data is kept in the main memory. TEMPORARY − Temporary tables are deleted while closing or opening a database. Basically, temporary tables are of two types − GLOBAL type − Accessible by all connections. LOCAL type − Accessible by the current connection. The default type for temporary tables is global type. Indexes of temporary tables are kept in the main memory, unless the temporary table is created using CREATE CACHED TABLE. ENGINE − The ENGINE option is only required when custom table implementations are used. NOT PERSISTENT − It is a modifier to keep the complete table data in-memory and all rows are lost when the database is closed. TRANSACTIONAL − It is a keyword that commits an open transaction and this command supports only temporary tables. Example In this example, let us create a table named tutorials_tbl using the following given data. Sr.No Column Name Data Type 1 ID Int 2 Title Varchar(50) 3 Author Varchar(20) 4 Submission_date Date The following query is used to create a table tutorials_tbl along with the given column data. CREATE TABLE tutorials_tbl ( id INT NOT NULL, title VARCHAR(50) NOT NULL, author VARCHAR(20) NOT NULL, submission_date DATE ); The above query produces the following output. (0) rows effected Create Schema Create Schema is a command used to create a user-dependent schema under a particular authorization (under the currently registered user). Syntax Following is the generic syntax of the Create Schema command. CREATE SCHEMA [ IF NOT EXISTS ] name [ AUTHORIZATION ownerUserName ] In the above generic syntax, AUTHORIZATION is a keyword used to provide the respective user name. This command is optional which means if we are not providing the user name, then it will consider the current user. The user that executes the command must have admin rights, as well as the owner. This command commits an open transaction in this connection. Example In this example, let us create a schema named test_schema under SA user, using the following command. CREATE SCHEMA test_schema AUTHORIZATION sa; The above command produces the following output. (0) rows effected Create Sequence Sequence is concept which is used to generate a number by following a sequence for id or any random column values. Syntax Following is the generic syntax of the create sequence command. CREATE SEQUENCE [ IF NOT EXISTS ] newSequenceName [ START WITH long ] [ INCREMENT BY long ] [ MINVALUE long | NOMINVALUE | NO MINVALUE ] [ MAXVALUE long | NOMAXVALUE | NO MAXVALUE ] [ CYCLE long | NOCYCLE | NO CYCLE ] [ CACHE long | NOCACHE | NO CACHE ] This generic syntax is used to create a sequence. The datatype of a sequence is BIGINT. In this the sequence, values are never re-used, even when the transaction is roll backed. Example In this example, let us create a sequence named SEQ_ID, using the following query. CREATE SEQUENCE SEQ_ID; The above query produces the following output. (0) rows effected Print Page Previous Next Advertisements ”;

H2 Database – Introduction ”; Previous Next H2 is an open-source lightweight Java database. It can be embedded in Java applications or run in the client-server mode. Mainly, H2 database can be configured to run as inmemory database, which means that data will not persist on the disk. Because of embedded database it is not used for production development, but mostly used for development and testing. This database can be used in embedded mode or in server mode. Following are the main features of H2 database − Extremely fast, open source, JDBC API Available in embedded and server modes; in-memory databases Browser-based Console application Small footprint − Around 1.5MB jar file size Features of H2 Database The main features of H2 Database are as follows − It is an extremely fast database engine. H2 is open source and written in Java. It supports standard SQL and JDBC API. It can use PostgreSQL ODBC driver too. It has embedded and Server mode. H2 supports clustering and multi-version concurrency. It has strong security features. Additional Features Following are some additional features of H2 Database − H2 is a disk-based or in-memory databases and tables, read-only database support, temporary tables. H2 provides transaction support (read committed), 2-phase-commit multiple connections, table level locking. H2 is a cost-based optimizer, using a genetic algorithm for complex queries, zeroadministration. H2 contains scrollable and updatable result set support, large result set, external result sorting, functions can return a result set. H2 supports encrypted database (AES), SHA-256 password encryption, encryption functions, and SSL. Components in H2 Database In order to use H2 Database, you need to have the following components − A web browser A H2 console server This is a client/server application, so both server and client (a browser) are required to run it. Print Page Previous Next Advertisements ”;

H2 Database Tutorial PDF Version Quick Guide Resources Job Search Discussion H2 is an open-source lightweight Java database. It can be embedded in Java applications or run in the client-server mode. H2 database can be configured to run as in-memory database, which means that data will not persist on the disk. In this brief tutorial, we will look closely at the various features of H2 and its commands, one of the best open-source, multi-model, next generation SQL product. Audience This tutorial is designed for all those software professionals who would like to learn how to use H2 database in simple and easy steps. This tutorial will give you a good overall understanding on the basic concepts of H2 database. Prerequisites H2 database primarily deals with relational data. Hence, you should first of all have a good understanding of the concepts of databases in general, especially RDBMS concepts, before going ahead with this tutorial. Print Page Previous Next Advertisements ”;

H2 Database – Select ”; Previous Next Select command is used to fetch record data from a table or multiple tables. If we design a select query, then it returns data in the form of result table called result sets. Syntax The basic syntax of SELECT statement is as follows − SELECT [ TOP term ] [ DISTINCT | ALL ] selectExpression [,…] FROM tableExpression [,…] [ WHERE expression ] [ GROUP BY expression [,…] ] [ HAVING expression ] [ { UNION [ ALL ] | MINUS | EXCEPT | INTERSECT } select ] [ ORDER BY order [,…] ] [ [ LIMIT expression ] [ OFFSET expression ] [ SAMPLE_SIZE rowCountInt ] ] [ FOR UPDATE ] To fetch all the available fields, use the following syntax. SELECT * FROM table_name; Example Consider the CUSTOMER table having the following records − +—-+———-+—–+———–+———-+ | ID | NAME | AGE | ADDRESS | SALARY | +—-+———-+—–+———–+———-+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +—-+———-+—–+———–+———-+ To get the customer table along with the given data, execute the following queries. CREATE TABLE CUSTOMER (id number, name varchar(20), age number, address varchar(20), salary number); INSERT into CUSTOMER values (1, ”Ramesh”, 32, ”Ahmedabad”, 2000); INSERT into CUSTOMER values (2, ”Khilan”, 25, ”Delhi”, 1500); INSERT into CUSTOMER values (3, ”kaushik”, 23, ”Kota”, 2000); INSERT into CUSTOMER values (4, ”Chaitali”, 25, ”Mumbai”, 6500); INSERT into CUSTOMER values (5, ”Hardik”, 27, ”Bhopal”, 8500); INSERT into CUSTOMER values (6, ”Komal”, 22, ”MP”, 4500); INSERT into CUSTOMER values (7, ”Muffy”, 24, ”Indore”, 10000); The following command is an example, which would fetch ID, Name and Salary fields of the customers available in the CUSTOMER table. SELECT ID, NAME, SALARY FROM CUSTOMERS; The above command produces the following result. +—-+———-+———-+ | ID | NAME | SALARY | +—-+———-+———-+ | 1 | Ramesh | 2000.00 | | 2 | Khilan | 1500.00 | | 3 | kaushik | 2000.00 | | 4 | Chaitali | 6500.00 | | 5 | Hardik | 8500.00 | | 6 | Komal | 4500.00 | | 7 | Muffy | 10000.00 | +—-+———-+———-+ Use the following query to fetch all the fields of CUSTOMERS table. SQL> SELECT * FROM CUSTOMERS; The above query produces the following result − +—-+———-+—–+———–+———-+ | ID | NAME | AGE | ADDRESS | SALARY | +—-+———-+—–+———–+———-+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +—-+———-+—–+———–+———-+ Print Page Previous Next Advertisements ”;

H2 Database – Delete ”; Previous Next The SQL DELETE query is used to delete the existing records from a table. We can use WHERE clause with DELETE query to delete selected records, otherwise all the records will be deleted. Syntax Following is the generic query syntax of the delete command. DELETE [ TOP term ] FROM tableName [ WHERE expression ] [ LIMIT term ] The above syntax deletes the rows from a table. If TOP or LIMIT is specified, at most the specified number of rows are deleted (no limit if null or smaller than zero). Example Consider the CUSTOMER table having the following records. +—-+———-+—–+———–+———-+ | ID | NAME | AGE | ADDRESS | SALARY | +—-+———-+—–+———–+———-+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +—-+———-+—–+———–+———-+ The following command will delete the details of the customer, whose ID is 6. DELETE FROM CUSTOMERS WHERE ID = 6; After execution of the above command, check the Customer table by executing the following command. SELECT * FROM CUSTOMERS; The above command produces the following output − +—-+———-+—–+———–+———-+ | ID | NAME | AGE | ADDRESS | SALARY | +—-+———-+—–+———–+———-+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +—-+———-+—–+———–+———-+ If we want to DELETE all the records from CUSTOMERS table, we do not use WHERE clause. The DELETE query would be as follows. DELETE FROM CUSTOMER; After executing the above command, no records will be available in the Customer table. Print Page Previous Next Advertisements ”;

H2 Database – Alter ”; Previous Next ALTER is a command used to change the table structure by adding different clauses to the alter command. Based on the scenario, we need to add respective clause to the alter command. In this chapter, we will discuss various scenarios of alter command. Alter Table Add Alter Table Add is a command used to add a new column to a table along with the respective data type. This command commits the transaction in this connection. Syntax Following is the generic syntax of the Alter Table Add command. ALTER TABLE [ IF EXISTS ] tableName ADD [ COLUMN ] { [ IF NOT EXISTS ] columnDefinition [ { BEFORE | AFTER } columnName ] | ( { columnDefinition } [,…] ) } Example In this example, we will add a new column start_date to the table tutorials_tbl. The datatype for start_date is Date. Following is the query to add a new column. ALTER TABLE tutorials_tbl ADD start_date DATE; The above query produces the following output. (6) rows effected Alter Table Add Constraint Alter table add constraint is a command used to add different constraints to the table such as primary key, foreign key, not null, etc. The required indexes are automatically created if they don’t exist yet. It is not possible to disable checking for unique constraint. This command commits an open transaction in this connection. Syntax Following is the generic syntax of the Alter table add constraint command. ALTER TABLE [ IF EXISTS ] tableName ADD constraint [ CHECK | NOCHECK ] Example In this example, let us add a primary key constraint (tutorials_tbl_pk) to the column id of the table tutorials_tbl, using the following query. ALTER TABLE tutorials_tbl ADD CONSTRAINT tutorials_tbl_pk PRIMARYKEY(id); The above query produces the following output. (6) row (s) effected Alter Table Rename Constraint This command is used to rename the constraint name of a particular relation table. This command commits an open transaction in this connection. Syntax Following is the generic syntax of the Alter Table Rename Constraint command. ALTER TABLE [ IF EXISTS ] tableName RENAME oldConstraintName TO newConstraintName While using this syntax, make sure that the old constraint name should exist with the respective column. Example In this example, we will change the primary key constraint name of the table tutorials_tbl from tutorials_tbl_pk to tutorials_tbl_pk_constraint. Following is the query to do so. ALTER TABLE tutorials_tbl RENAME CONSTRAINT tutorials_tbl_pk TO tutorials_tbl_pk_constraint; The above query produces the following output. (1) row (s) effected Alter Table Alter Column This command is used to change the structure and properties of the column of a particular table. Changing the properties means changing the datatype of a column, rename a column, change the identity value, or change the selectivity. Syntax Following is the generic syntax of the Alter Table Alter Column command. ALTER TABLE [ IF EXISTS ] tableName ALTER COLUMN columnName { { dataType [ DEFAULT expression ] [ [ NOT ] NULL ] [ AUTO_INCREMENT | IDENTITY ] } | { RENAME TO name } | { RESTART WITH long } | { SELECTIVITY int } | { SET DEFAULT expression } | { SET NULL } | { SET NOT NULL } } In the above syntax − RESTART − command changes the next value of an auto increment column. SELECTIVITY − command sets the selectivity (1-100) for a column. Based on the selectivity value we can image the value of the column. SET DEFAULT − changes the default value of a column. SET NULL − sets the column to allow NULL. SET NOT NULL − sets the column to allow NOT NULL. Example In this example, we will rename the column of the table tutorials_tbl from Title to Tutorial_Title using the following query. ALTER TABLE tutorials_tbl ALTER COLUMN title RENAME TO tutorial_title; The above query produces the following output. (0) row(s) effected In a similar way, we can perform different scenarios with the ALTER command. Print Page Previous Next Advertisements ”;

H2 Database – Update ”; Previous Next The UPDATE query is used to update or modify the existing records in a table. We can use WHERE clause with UPDATE query to update the selected rows, otherwise all the rows would be affected. Syntax Following is the basic syntax of the UPDATE query. UPDATE tableName [ [ AS ] newTableAlias ] SET { { columnName = { DEFAULT | expression } } [,…] } | { ( columnName [,…] ) = ( select ) } [ WHERE expression ] [ ORDER BY order [,…] ] [ LIMIT expression ] In this UPDATE syntax, we can combine more than one condition by using AND or OR clauses. Example Consider the CUSTOMER table having the following records. +—-+———-+—–+———–+———-+ | ID | NAME | AGE | ADDRESS | SALARY | +—-+———-+—–+———–+———-+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +—-+———-+—–+———–+———-+ If you want to get the customer table along with the given data, execute the following queries. CREATE TABLE CUSTOMER (id number, name varchar(20), age number, address varchar(20), salary number); INSERT into CUSTOMER values (1, ”Ramesh”, 32, ”Ahmedabad”, 2000); INSERT into CUSTOMER values (2, ”Khilan”, 25, ”Delhi”, 1500); INSERT into CUSTOMER values (3, ”kaushik”, 23, ”Kota”, 2000); INSERT into CUSTOMER values (4, ”Chaitali”, 25, ”Mumbai”, 6500); INSERT into CUSTOMER values (5, ”Hardik”, 27, ”Bhopal”, 8500); INSERT into CUSTOMER values (6, ”Komal”, 22, ”MP”, 4500); INSERT into CUSTOMER values (7, ”Muffy”, 24, ”Indore”, 10000); The following command is an example, which would update ADDRESS for a customer whose ID is 6 − UPDATE CUSTOMERS SET ADDRESS = ”Pune” WHERE ID = 6; Now, CUSTOMERS table would have the following records. We can check the customer table records by executing the following query. SELECT * FROM CUSTOMERS; The above query produces the following result. +—-+———-+—–+———–+———-+ | ID | NAME | AGE | ADDRESS | SALARY | +—-+———-+—–+———–+———-+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | Pune | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +—-+———-+—–+———–+———-+ To modify all ADDRESS and SALARY column values in CUSTOMERS table, we need not use the WHERE clause. The UPDATE query would be as follows − UPDATE CUSTOMERS SET ADDRESS = ”Pune”, SALARY = 1000.00; Now, CUSTOMERS table would have the following records. We can check the customer table records by executing the following query. SELECT * FROM CUSTOMERS; The above query produces the following result − +—-+———-+—–+———+———+ | ID | NAME | AGE | ADDRESS | SALARY | +—-+———-+—–+———+———+ | 1 | Ramesh | 32 | Pune | 1000.00 | | 2 | Khilan | 25 | Pune | 1000.00 | | 3 | kaushik | 23 | Pune | 1000.00 | | 4 | Chaitali | 25 | Pune | 1000.00 | | 5 | Hardik | 27 | Pune | 1000.00 | | 6 | Komal | 22 | Pune | 1000.00 | | 7 | Muffy | 24 | Pune | 1000.00 | +—-+———-+—–+———+———+ Print Page Previous Next Advertisements ”;

H2 Database – Backup ”; Previous Next BACKUP is the command used to take database backup into a separate .zip file. Objects are not locked, and when it takes backup the transaction log is also copied. Admin rights are required to execute this command. Syntax Following is the generic syntax of the Backup command. BACKUP TO fileNameString; Example In this example, let us take a backup of the current database into backup.zip file. Use the following command for the same. BACKUP TO ”backup.zip”; On executing the above command, you will get the backup.zip file in your local file system. Print Page Previous Next Advertisements ”;