Oracle DBA FAQ - Understanding SQL DML Statements

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By: FYIcenter.com

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How To Omit Columns with Default Values in INSERT Statement?

If you don't want to specify values for columns that have default values, or you want to specify values to columns in an order different than how they are defined, you can provide a column list in the INSERT statement. If a column is omitted in the column, Oracle applies 3 rules:

If default value is defined for the column, that default value will be used.
If no default value is defined for the column and NULL is allowed, NULL will be used.
If no default value is defined for the column and NULL is not allowed, error will be returned.

The following tutorial exercise gives a good example:

INSERT INTO fyi_links (url, id) 
  VALUES ('http://sqa.fyicenter.com', 103);
1 row created.

SELECT * FROM fyi_links;
   ID URL                      NOTES     COUNTS CREATED
----- ------------------------ -------- ------- ---------
  101 http://dev.fyicenter.com NULL           0 30-Apr-06
  102 http://dba.fyicenter.com NULL           0 07-MAY-06
  103 http://sqa.fyicenter.com NULL     NULL    07-MAY-06

How To Insert Multiple Rows with One INSERT Statement?

If you want to insert multiple rows with a single INSERT statement, you can use a subquery instead of the VALUES clause. Rows returned from the subquery will be inserted the target table.

The following tutorial exercise gives a good example:

INSERT INTO fyi_links
  SELECT department_id, department_name||'.com', NULL, NULL,
    SYSDATE FROM departments WHERE department_id >= 250;
3 row created.

SELECT * FROM fyi_links;
   ID URL                      NOTES     COUNTS CREATED
----- ------------------------ -------- ------- ---------
  101 http://dev.fyicenter.com NULL           0 30-Apr-06
  102 http://dba.fyicenter.com NULL           0 07-MAY-06
  103 http://sqa.fyicenter.com NULL     NULL    07-MAY-06  
  250 Retail Sales.com         NULL     NULL    07-MAY-06
  260 Recruiting.com           NULL     NULL    07-MAY-06
  270 Payroll.com              NULL     NULL    07-MAY-06

How To Update Values in a Table?

If you want to update some values in one row or multiple rows in a table, you can use the UPDATE statement. The script below shows a good example:

UPDATE fyi_links SET counts = 999, notes = 'Good site.' 
  WHERE id = 101;
1 row updated.

SELECT * FROM fyi_links WHERE id = 101;
  ID URL                      NOTES      COUNTS CREATED
---- ------------------------ ---------- ------ ---------
 101 http://dev.fyicenter.com Good site.    999 07-MAY-06

How To Update Values on Multiple Rows?

If the WHERE clause in an UPDATE matches multiple rows, the SET clause will be applied to all matched rows. This rule allows you to update values on multiple rows in a single UPDATE statement. Here is a good example:

UPDATE fyi_links SET counts = 9, notes = 'Wrong URL' 
  WHERE id >= 250;
3 rows updated.

SELECT * FROM fyi_links WHERE id >= 250;
   ID URL                  NOTES         COUNTS CREATED
----- -------------------- ------------ ------- ---------
  250 Retail Sales.com     Wrong URL          9 07-MAY-06
  260 Recruiting.com       Wrong URL          9 07-MAY-06
  270 Payroll.com          Wrong URL          9 07-MAY-06

This statement updated 3 rows with the same new values on all 3 rows.

How To Use Existing Values in UPDATE Statements?

If a row matches the WHERE clause in a UPDATE statement, existing values in this row can be used in expressions to provide new values in the SET clause. Existing values are represented by columns in the expressions. The tutorial exercise below shows a good example:

UPDATE fyi_links SET id = 1000 + id, counts = id*2 
  WHERE id >= 250;
3 rows updated.

SELECT * FROM fyi_links WHERE id >= 250;
   ID URL                  NOTES         COUNTS CREATED
----- -------------------- ------------ ------- ---------
 1250 Retail Sales.com     Wrong URL        500 07-MAY-06
 1260 Recruiting.com       Wrong URL        520 07-MAY-06
 1270 Payroll.com          Wrong URL        540 07-MAY-06

This statement increased values in the id column by 1000.

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