Teradata SubQueries

The Teradata SubQuery returns records from one table based on the values from another table.

It is a SELECT query within another query. The SELECT query called the inner query is executed first, and the outer query uses the result. Some of its most important features are:

A query can have multiple SubQueries, and SubQueries may contain another SubQuery.
SubQueries do not return the duplicate records.
If SubQuery returns only one value, then we can use = operator to use it with the outer query. If it returns multiple values, then we can use IN or NOT IN.
The SubQueries must be enclosed with parenthesis.

Syntax

Following is the generic syntax of Teradata SubQueries.

SELECT col1, col2, col3,...
FROM  
Outer Table 
WHERE col1 OPERATOR (Inner SELECT Query);

Example

Consider the following Salary table of the employees.

Employee_Id Gross	Deduction	NetPay
1001	40,000	4,000	36,000
1002	80,000	6,000	74,000
1003	90,000	7,000	83,000
1004	75,000	5,000	70,000

The following query identifies the employee Id with the highest salary. The inner SELECT performs the aggregation function to return the maximum NetPay value, and the outer SELECT query uses this value to return the employee record with this value.

SELECT Employee_Id, NetPay 
FROM Salary 
WHERE NetPay =  
(SELECT MAX(NetPay)  
FROM Salary);

When this query is executed, it produces the following output.

     /* Query completed. One row found. 2 columns returned  */
     /* Total elapsed time was 1 second */

 Employee_Id        NetPay 
 
     1003            83000

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