E051-08, “Correlation names in the FROM clause”

1. Only without as: FROM tbl AS t
2. Only without as: FROM tbl AS t, exceptions exist: FROM JSON_TABLE(…) AS t

SQL allows renaming tables in from and join clauses by providing the optional keyword as followed by the new table name. The table is only known by its new name in the clauses that follow in order of logical evaluation.

SELECT …
  FROM tbl_a [AS] a
  JOIN tbl_b [AS] b

The SQL standard requires every table in from and join to have a name. Therefore, tables that don’t have a natural name—such as sub-queries—must use this syntax to assign a name.

Extensions

Some systems allow omitting a table name where the standard requires one.

Related

Tutorials

• Renaming Tables And Columns in the FROM Clause

Related Features

• E051-05, “Select list items can be renamed”

• E051-09, “Rename columns in the FROM clause”

Normative References

E051-08, “Correlation names in the FROM clause”, is a mandatory feature of ISO/IEC 9075-2:2023. It already appeared in ANSI X3.135-1989 but without the optional keyword as, which was introduced with ISO/IEC 9075:1992 as part of the level “intermediate”. Accepting the keyword as became mandatory with ISO/IEC 9075-2:1999.