Wild Card Characters and Sub Queries -- Sql Server

  In SQL, wildcard characters are used with the SQL LIKE operator.

SQL wildcards are used to search for data within a table. 

  With SQL, the wildcards are:

Wildcard	Description
%	A substitute for zero or more characters
_	A substitute for a single character
[charlist]	Sets and ranges of characters to match
[^charlist] or [!charlist]	Matches only a character NOT specified within the brackets

Sub Queries

A Sub query or Inner query or Nested query is a query within another SQL query and embedded within the WHERE clause.

A sub query is used to return data that will be used in the main query as a condition to further restrict the data to be retrieved.

Subqueries can be used with the SELECT, INSERT, UPDATE, and DELETE statements along with the operators like =, <, >, >=, <=, IN, BETWEEN etc.

There are a few rules that subqueries must follow:

•        Subqueries must be enclosed within parentheses.
•        A sub query can have only one column in the SELECT clause, unless multiple columns are in the main query for the sub query to compare its selected columns.
•        An ORDER BY cannot be used in a sub query, although the main query can use an ORDER BY. The GROUP BY can be used to perform the same function as the ORDER BY in a sub query.
•        Subqueries that return more than one row can only be used with multiple value operators, such as the IN operator.
•      The SELECT list cannot include any references to values that evaluate to a BLOB, ARRAY, CLOB, or NCLOB.
•      A sub query cannot be immediately enclosed in a set function.
•     The BETWEEN operator cannot be used with a sub query; however, the BETWEEN operator can be used within the sub query.

Subqueries with the SELECT Statement:

Subqueries are most frequently used with the SELECT statement. The basic syntax is as follows:

SELECT column_name [, column_name ]

FROM   table1 [, table2 ]

WHERE  column_name OPERATOR

      (SELECT column_name [, column_name ]

      FROM table1 [, table2 ]

      [WHERE])

Subqueries with the INSERT Statement:

Subqueries also can be used with INSERT statements. The INSERT statement uses the data returned from the subquery to insert into another table.

The selected data in the subquery can be modified with any of the character, date or number functions.

The basic syntax is as follows:

INSERT INTO table_name [ (column1 [, column2 ]) ]

           SELECT [ *|column1 [, column2 ]

           FROM table1 [, table2 ]

           [ WHERE VALUE OPERATOR ]

 

Subqueries with the UPDATE Statement:

The sub query can be used in conjunction with the UPDATE statement. Either single or multiple columns in a table can be updated when using a sub query with the UPDATE statement.

The basic syntax is as follows:

UPDATE table

SET column_name = new_value

[ WHERE OPERATOR [ VALUE ]

   (SELECT COLUMN_NAME

   FROM TABLE_NAME)

   [ WHERE) ]

Subqueries with the DELETE Statement:

The subquery can be used in conjunction with the DELETE statement like with any other statements mentioned above.

The basic syntax is as follows:

DELETE FROM TABLE_NAME

[ WHERE OPERATOR [ VALUE ]

   (SELECT COLUMN_NAME

   FROM TABLE_NAME)

   [ WHERE) ]