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Alter database using alter database in SQL.txt

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+// Alter database using alter database
+Alter database enables you to change the overall characteristics of a database.
+These characteristics are stored in the db.opt file in the database directory. 
+to use ALTER DATABASE, you need the ALTER privilege on the database.
+ALTER SCHEMA is a synonym for ALTER DATABASE.
+The database name can be omitted from the syntax in which case the statemnet
+applies to the default database.
+Syntax: ALTER DATABASE database_name;

Change Column Name and Its Data Type Without Constraints in SQL.txt

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+// Change column:
+This is used to change name and data type of an existing column. without constraints
+syntax: ALTER TABLE  table_name CHANGE COLUMN old_column_name new_column_name new data_type(size);
+
+ex: ALTER TABLE new CHANGE COLUMN name student varchar(20);
+Query OK, 0 rows affected (0.01 sec)
+Records: 0  Duplicates: 0  Warnings: 0
+mysql> desc new;
++----------+-------------+------+-----+---------+----------------+
+| Field    | Type        | Null | Key | Default | Extra          |
++----------+-------------+------+-----+---------+----------------+
+| t_id     | int         | YES  |     | NULL    |                |
+| id       | int         | NO   | PRI | NULL    | auto_increment |
+| student  | varchar(20) | YES  |     | NULL    |                |
+| t_number | int         | YES  | UNI | NULL    |                |
+| address  | varchar(50) | YES  |     | NULL    |                |
+| number   | int         | YES  |     | NULL    |                |
+| s_id     | int         | NO   |     | NULL    |                |
++----------+-------------+------+-----+---------+----------------+

Change Column name and its Data type with constraint in SQL.txt

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+// Change Column name and its Data type with constraint
+Change column with Constraints:-
+syntax: ALTER TABLE table_name CHANGE COLUMN old_column_name new_column new _datetype (size) Constraint_name, 
+ADD Constraint_name (column_name);
+
+ex: ALTER TABLE staff CHANGE COLUMN s_id id int NOT NULL, ADD PRIMARY KEY
+(id);
+Query OK, 1 row affected (0.08 sec)
+Records: 1  Duplicates: 0  Warnings: 0
+
+mysql> desc staff;
++--------+-------------+------+-----+---------+-------+
+| Field  | Type        | Null | Key | Default | Extra |
++--------+-------------+------+-----+---------+-------+
+| id     | int         | NO   | PRI | NULL    |       |
+| name   | varchar(50) | YES  |     | NULL    |       |
+| number | int         | YES  |     | NULL    |       |
++--------+-------------+------+-----+---------+-------+

Change more than one column Name and Its data type without constraints in SQL.txt

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+//Change more than one column Name and Its data type without constraints in SQL.
+syntax: ALTER TABLE table_name CHANGE COLUMN old_column_name new_column_name new_datatype(size);
+CHANGE COLUMN old_column_name new_column_name new_datatype(size);
+ex: ALTER TABLE new CHANGE COLUMN t_id teacher_id int (10), CHANGE COLUMN
+ id student_id int(10);
+Query OK, 4 rows affected, 2 warnings (0.08 sec)
+Records: 4  Duplicates: 0  Warnings: 2
+
+mysql> desc new;
++------------+-------------+------+-----+---------+-------+
+| Field      | Type        | Null | Key | Default | Extra |
++------------+-------------+------+-----+---------+-------+
+| teacher_id | int         | YES  |     | NULL    |       |
+| student_id | int         | NO   | PRI | NULL    |       |
+| student    | varchar(20) | YES  |     | NULL    |       |
+| t_number   | int         | YES  | UNI | NULL    |       |
+| address    | varchar(50) | YES  |     | NULL    |       |
+| number     | int         | YES  |     | NULL    |       |
+| s_id       | int         | NO   |     | NULL    |       |
++------------+-------------+------+-----+---------+-------+

Delete Data sof Table using Truncate Table in SQL.txt

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+//Delete data of table using Truncate table.
+-> when we only want to delete the data inside the table, and not the table itself.
+syntax: TRUNCATE TABLE table_name;
+ex:select * from student;
++-------------+------+---------+
+| name        | roll | address |
++-------------+------+---------+
+| U'I Testing |  101 | Ktm     |
++-------------+------+---------+
+1 row in set (0.02 sec)
+
+mysql> TRUNCATE TABLE student;
+Query OK, 0 rows affected (0.02 sec)
+
+mysql> select * from student;
+Empty set (0.00 sec)

Drop Column with or without constraint in SQL.txt

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+//Drop Column with or without constraint
+-> When a column a table need to delete.
+syntax : ALTER TABLE table_name DROP COLUMN column_name;
+ex:ALTER TABLE staff DROP COLUMN number;
+->  desc staff;
++-------+----------+------+-----+---------+-------+
+| Field | Type     | Null | Key | Default | Extra |
++-------+----------+------+-----+---------+-------+
+| id    | int      | NO   | PRI | NULL    |       |
+| name  | char(20) | YES  |     | NULL    |       |
++-------+----------+------+-----+---------+-------+
+
+// When removing constraint from a column.
+syntax: ALTER TABLE table_name DROP constraint_name column_name;

Drop Table or Delete Table from Database in SQL.txt

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+// Drop Table or Delete Table from Database.
+-> This command is used to delete/remove table from the database;
+syntax: DROP TABLE table_name;
+ex: show tables;
++-----------------+
+| Tables_in_my_db |
++-----------------+
+| new             |
+| staff           |
+| student         |
+| student_rec     |
+| student_reg     |
++-----------------+
+5 rows in set (0.00 sec)
+
+mysql> drop table student_rec;
+Query OK, 0 rows affected (0.01 sec)
+
+mysql> show tables;
++-----------------+
+| Tables_in_my_db |
++-----------------+
+| new             |
+| staff           |
+| student         |
+| student_reg     |
++-----------------+

Rename table name using Rename table in SQL.txt

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+//Rename table name using Rename table
+-> This command is used to rename one or more table.
+syntax: RENAME TABLE old_table_name to new_table_name;
+ex: RENAME TABLE staff TO emp;
+mysql> show tables;
++-----------------+
+| Tables_in_my_db |
++-----------------+
+| emp             |
+| new             |
+| student         |
+| student_reg     |
++-----------------+

modify column data typeand its size with or without constraint in SQL.txt

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+Modify Column Data Type Its size with or Without Constraint
+-> This is used to modify size of the data type or the data type it self of an existing column without changing column name.
+syntax:ALTER TABLE table_name MODIFY COLUMN column_name datatype(size);
+ex: ALTER TABLE staff MODIFY COLUMN name char(20);
+Query OK, 1 row affected (0.08 sec)
+Records: 1  Duplicates: 0  Warnings: 0
+
+mysql> desc staff;
++--------+----------+------+-----+---------+-------+
+| Field  | Type     | Null | Key | Default | Extra |
++--------+----------+------+-----+---------+-------+
+| id     | int      | NO   | PRI | NULL    |       |
+| name   | char(20) | YES  |     | NULL    |       |
+| number | int      | YES  |     | NULL    |       |
++--------+----------+------+-----+---------+-------+