MySQL Manual Version 5.0.20-MySQL Optimization (2) (1) (4)_PHP Tutorial

The following example shows how to use the information provided by EXPLAIN to maximize the performance of multi-table joint queries.

Suppose you have the following SELECT statement and are planning to use EXPLAIN to detect it:

EXPLAIN SELECT tt.TicketNumber, tt.TimeIn,

tt.ProjectReference, tt.EstimatedShipDate,

tt.ActualShipDate, tt.ClientID,

tt.ServiceCodes, tt.RepetitiveID,

tt.CurrentProcess, tt.CurrentDPPerson,

tt.RecordVolume, tt.DPPrinted, et.COUNTRY,

et_1.COUNTRY, do.CUSTNAME

FROM tt, et, et AS et_1, do

WHERE tt.SubmitTime IS NULL

AND tt.ActualPC = et.EMPLOYID

AND tt.AssignedPC = et_1.EMPLOYID

AND tt. ClientID = do.CUSTNMBR;

In this example, first make the following assumptions:

The fields to be compared are defined as follows:

(t114)

http://www.bkjia.com/PHPjc/630970.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/630970.htmlTechArticleThe following example shows how to use the information provided by EXPLAIN to maximize the performance of multi-table joint queries. Suppose you have the following SELECT statement and are planning to use EXPLAIN to detect it: ...