MySQL Articles - Page 382 of 402

On specifying a CHARACTER SET binary attribute for a character string data type, MySQL creates that column as its subsequent binary string type. The conversions for CHAR, VARCHAR and BLOB data types take place as follows −CHAR would become BINARYVARCHAR would become VARBINARYTEXT would become BLOBThe above kind of conversion does not occur for ENUM and SET data type and they both are created as declared while creating the table.ExampleIn the example below we have created a table named ‘EMP’ with four columns all specified as CHARACTER SET binary as follows −mysql> Create table Emp(Name varchar(10) CHARACTER SET binary, Address ... Read More

With the help of the following MySQL query we can check the character sets of all the tables in a particular database −mysql> Select Column_name, TABLE_NAME, CHARACTER_SET_NAME FROM        INFORMATION_SCHEMA.Columns Where TABLE_SCHEMA = 'db_name';ExampleFor example, the query below returns the character sets of all the tables along with the column names in a database named ‘Alpha’.mysql> Select Column_name 'Column', TABLE_NAME, CHARACTER_SET_NAME FROM INFORMATION_SCHEMA.Columns Where TABLE_SCHEMA = 'Alpha'; +---------+------------+--------------------+ | Column  | TABLE_NAME | CHARACTER_SET_NAME | +---------+------------+--------------------+ | Name    | employee   | latin1             | | email   | employee   ... Read More

With the help of the following MySQL query we can check the character sets of all the tables in a particular database −mysql> Select TABLE_NAME, CHARACTER_SET_NAME FROM INFORMATION_SCHEMA.Columns Where TABLE_SCHEMA = 'db_name';ExampleFor example, the query below returns the character sets of all the tables in a database named ‘Alpha’.mysql> Select TABLE_NAME, CHARACTER_SET_NAME FROM INFORMATION_SCHEMA.Columns Where TABLE_SCHEMA = 'Alpha'; +------------+--------------------+ | TABLE_NAME | CHARACTER_SET_NAME | +------------+--------------------+ | employee   | latin1             | | employee   | latin1             | | student    | latin1             ... Read More

We can use DELETE statement along with a WHERE clause, which identifies those multiple rows, to delete multiple rows from MySQL table.Examplemysql> Select * from names; +------+-----------+ | id   | name      | +------+-----------+ | 1    | Rahul     | | 2    | Gaurav    | | 3    | Raman     | | 5    | Ram       | +------+-----------+ 4 rows in set (0.00 sec) mysql> DELETE from names WHERE id > 2; Query OK, 2 rows affected (0.04 sec)The query above will delete multiple rows because WHERE clause identify two rows having id > 2 from table ‘names’.mysql> Select * from names; +------+-----------+ | id   | name      | +------+-----------+ | 1    | Rahul     | | 2    | Gaurav    | +------+-----------+ 2 rows in set (0.00 sec)

Following is the query to check character set of the columns of MySQL table −mysql> Select Column_name 'Column', Character_set_name 'Charset' FROM        information_schema.columns where table_schema = 'db_name' and        table_name ='table_name';ExampleFor example, the query below returns the name of the columns of ‘test_char_set’ table in a database named ‘sample’ along with the character sets of those columns.mysql> Select Column_name 'Column', Character_set_name 'Charset' FROM        information_schema.columns where table_schema = 'Sample' and        table_name ='test_char_set'; +--------+---------+ | Column | Charset | +--------+---------+ | Name   | latin1  | | Field  | latin1  | ... Read More

Following is the query to check default character set of the particular MySQL database −mysql> SELECT SCHEMA_NAME 'DatabaseName', default_character_set_name 'Charset' FROM information_schema.SCHEMATA where schema_name = 'db_name';ExampleFor example, the query below will return the default character set of a database named ‘Sample’ −mysql> SELECT SCHEMA_NAME 'DatabaseName', default_character_set_name 'Charset' FROM information_schema.SCHEMATA where schema_name = 'Sample'; +----------------+---------+ | DatabaseName   | Charset | +----------------+---------+ | Sample         | latin1  | +----------------+---------+ 1 row in set (0.00 sec)

The query below will return the name of the database along with the default character set −mysql> SELECT SCHEMA_NAME 'Database', default_character_set_name 'charset' FROM information_schema.SCHEMATA; +--------------------+---------+ | Database           | Charset | +--------------------+---------+ | information_schema | utf8    | | gaurav             | latin1  | | menagerie          | latin1  | | mysql              | latin1  | | performance_schema | utf8    | | sample             | latin1  | | test               | latin1  | | tutorial           | latin1  | +--------------------+---------+ 8 rows in set (0.00 sec)

We can use DELETE statement along with a WHERE clause, which identifies that particular row, to delete a row from MySQL table.Examplemysql> Select * from names; +------+-----------+ | id   | name      | +------+-----------+ | 1    | Rahul     | | 2    | Gaurav    | | 3    | Raman     | | 4    | Aarav     | | 5    | Ram       | +------+-----------+ 5 rows in set (0.00 sec) mysql> DELETE from names where id = 4; Query OK, 1 row affected (0.07 sec)The query above will delete a single row having id = 4 from table ‘names’.mysql> Select * from names; +------+-----------+ | id   | name      | +------+-----------+ | 1    | Rahul     | | 2    | Gaurav    | | 3    | Raman     | | 5    | Ram       | +------+-----------+ 4 rows in set (0.00 sec)

With the help of DISTINCT keyword in SELECT statement, we can get the unique rows in MySQL result set.Examplemysql> Select * from names; +------+-----------+ | id   | name      | +------+-----------+ | 1    | Rahul     | | 2    | Gaurav    | | 3    | Raman     | | 4    | Aarav     | | 5    | Ram       | | 5    | Ram       | | 5    | Ram       | +------+-----------+ 7 rows in set (0.00 sec)As we can see that table ‘names’ is having three duplicate rows, with the help of following query we can get the result set having only unique rows.mysql> Select DISTINCT * from names; +------+-----------+ | id   | name      | +------+-----------+ | 1    | Rahul     | | 2    | Gaurav    | | 3    | Raman     | | 4    | Aarav     | | 5    | Ram       | +------+-----------+ 5 rows in set (0.00 sec)

In this case, MySQL will return an error message because we know that if sub-query is used to assign new values in the SET clause of UPDATE statement then it must return exactly one row for each row in the update table that matches the WHERE clause.Examplemysql> insert into info(id, remarks) values(5, 'average'); Query OK, 1 row affected (0.06 sec) mysql> select * from info; +------+-----------+ | id   | remarks   | +------+-----------+ | 1    | Good      | | 2    | Good      | | 3    | Excellent | | 4   ... Read More