The MAX of two MAX values in SQL

Digg This!     StumbleUpon     Del.icio.us

RELATED CONTENT SQL How to check SQL query construction with the Mimer Validator Using the SQL GROUP BY clause for counting combinations How to use an SQL CASE expression How to sort an SQL UNION query with special ORDER BY sequence How to use string functions to make an SQL join An SQL solution for a customer order homework problem How to use SQL's POSITION function with substrings Using SQL date functions to get totals for last three days Using CASE in the SQL ORDER BY clause What's the difference between an SQL inner join and equijoin? Oracle and SQL Using the SQL GROUP BY clause for counting combinations How to use an SQL CASE expression How to use the Oracle Database SQL Reference Manual How to use SQL Developer to run SQL statements How to work with the Oracle database home page How to use SQL*Plus in Oracle How to use SQL Developer to work with an Oracle database How to view and edit table column definitions How to sort an SQL UNION query with special ORDER BY sequence How to use string functions to make an SQL join Oracle and SQL Research

RELATED GLOSSARY TERMS Terms from Whatis.com − the technology online dictionary autonomous transaction  (SearchOracle.com) CFML  (SearchOracle.com) dynamic SQL  (SearchOracle.com) foreign key  (SearchOracle.com) Java Database Connectivity  (SearchOracle.com) Open Database Connectivity  (SearchOracle.com) Oracle  (SearchOracle.com) stored procedure  (SearchOracle.com) The Open Group  (SearchOracle.com)

RELATED RESOURCES 2020software.com, trial software downloads for accounting software, ERP software, CRM software and business software systems Search Bitpipe.com for the latest white papers and business webcasts Whatis.com, the online computer dictionary

The answer to your question is the GREATEST function. However, we must make a couple of small changes to your expressions to make the query work.

select greatest(
         ( select max(col1) from table1 )
       , ( select max(col2) from table2 )
               ) as col3 

Here each subquery produces a single value, and then GREATEST, which is a scalar function—as opposed to MAX, which is an aggregate function—selects the higher of those values.

If your particular database system does not support the standard SQL GREATEST function, use this:

select case when max1 > max2
            then max1
            else max2
        end as col3
  from ( select max(col1) as max1
           from table1 
       ) as t1
cross
  join ( select max(col2) as max2
           from table2 
       ) as t2 

Why a cross join? Because each of the derived tables (t1 and t2) returns only one row, so the cross join produces only one row, with two columns, max1 and max2.

Note that GREATEST can take any number of values. The CASE approach, however, becomes complex and cumbersome for more than two values.