DML
basically consists of 4 commands:
- INSERT
- INSERT-- SELECT
- UPDATE
- DELETE
INSERT: Used to
Insert a new row in the table.
Example:
INSERT INTO employee_table VALUES (121,
NULL, 4010, 41211, 'Sukul', 'Mahadik', 890303, 460421, 41000);
In the
above example we have entered values for all the columns . However we need not
provide values for all the columns as shown below. For the columns we don’t
provide a value will receive either
their assigned default value (as provided by the DEFAULT or WITH DEFAULT options in the CREATE TABLE
statement), or a NULL value if no default is specified but nulls are
allowed.
Caution: If the column for which we are no providing any value
does not accept NULL(defined as NOT NULL) then the insert will fail.
Example:
INSERT INTO employee (last_name, first_name, hire_date,
birthday, salary_amount, employee_number)
VALUES
('Sukul', 'Mahadik', 861027, 541110,76500.00, 1291);
INSERT SELECT: Used
to copy rows from one table to another.
Syntax:
INSERT INTO target_table SELECT * FROM source_table;
The SELECT portion
of the statement may be used to define a subset of rows and/or a subset of
columns to be inserted to the target table.
UPDATE: Allows you to
modify one or many columns of one or more rows in a table.
The
where clause qualifies the rows to be updated.
The
where clause of update query can include:
- Columns names being updated.
- Subqueries.
- Joins with columns from other table.
Simple update Example:
UPDATE EMPLOYEE_TABLE
SET SALARY = 1000
SET SALARY = 1000
WHERE EMPLOYEE_NUMBER= 85746 and EMPLOYEE_NAME='SUKUL;
Update using Subquery:
UPDATE EMPLOYEE_TABLE
SET SALARY = SALARY * 1.10
WHERE DEPARTMENT_NO IN (SELECT DEPTNO FROM DEPARTMENT_TABLE);
Update using Join:
UPDATE EMPLOYEE_TABLE
SET SALARY = SALARY * 1.10
WHERE EMPLOYEE_TABLE.DEPT_NO= DEPARTMENT.DEPT_NO
AND DEPARTMENT.DEPT_NAME LIKE '%SUPPORT%';
SET SALARY = SALARY * 1.10
WHERE EMPLOYEE_TABLE.DEPT_NO= DEPARTMENT.DEPT_NO
AND DEPARTMENT.DEPT_NAME LIKE '%SUPPORT%';
In an update, you can't use
the ON clause, so the join condition is specified in
the WHERE clause.
DELETE : Allows deleting rows from a table.
If we
don’t specify the where clause all the
rows will be deleted.
The
where clause of delete query can include:
- Columns names of the target table.
- Subqueries.
- Joins with columns from other table.
Simple Delete example:
DELETE
FROM employee
WHERE department_number = 301;
Deleting all rows:
DELETE
FROM employee ALL; /* Teradata syntax */
DELETE
FROM employee; /* ANSI standard syntax */
Deleting Using Subquery:
DELETE
FROM EMPLOYEE_TABLE WHERE DEPARTMENT_NO IN (SELECT DEPTNO FROM
DEPARTMENT_TABLE);
Deleting Using Join:
DELETE
FROM EMPLOYEE_TABLE
WHERE EMPLOYEE_TABLE.DEPT_NO= DEPARTMENT.DEPT_NO
AND DEPARTMENT.DEPT_NAME LIKE '%SUPPORT%';
AND DEPARTMENT.DEPT_NAME LIKE '%SUPPORT%';
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