Query Primer - Query Clauses

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There are several components or clauses that make up the select statement. While only one of them is mandatory when using MySQL (the selectclause), you will usually include at least two or three of the six available clauses. Table 3-1 shows the different clauses and their purposes.

Table 3-1. Query clauses

Clause name	Purpose
Select	Determines which columns to include in the query’s result set
From	Identifies the tables from which to draw data and how the tables should be joined
Where	Restricts the number of rows in the final result set
Group by	Used to group rows together by common column values
Having	Restricts the number of rows in the final result set using grouped data
Order by	Sorts the rows of the final result set by one or more columns

All of the clauses shown in Table 3-1 are included in the ANSI specification; additionally, there are several other clauses unique to MySQL that will be explored in Appendix B. The following sections delve into the uses of the six major query clauses.

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