SQL language references
SQL language reference
Firebird 4.0 Language Reference (23 May 2021, version 0.9)
Firebird 3.0 Language Reference (Version 0.15, 31 July 2021)
Firebird 2.5 Language Reference (27 April 2021, version 1.5)
Firebird 2.5 language reference update
Firebird 2.1 language reference update
Firebird 2.0 language reference update
InterBase 6.0 DSQL syntax