SQL Language Extension: SET BIND

Implements capability to setup columns coercion rules in current session.

Author:

Alex Peshkoff <peshkoff@mail.ru>

Syntax is:

SET BIND OF { type-from | TIME ZONE } TO { type-to | LEGACY | EXTENDED | NATIVE };

Description:

Makes it possible to define rules of describing types of returned to the client columns in non-standard way - type-from is replaced with type-to, automatic data coercion takes place.

When incomplete type definition is used (i.e. CHAR instead CHAR(n)) in left part of SET BIND coercion will take place for all CHAR columns, not only default CHAR(1). Special incomplete type TIME ZONE stands for all types (namely TIME & TIMESTAMP) WITH TIME ZONE. When incomplete type definiton is used in right side of the statement (TO part) firebird engine will define missing details about that type automatically based on source column.

Changing bind of any NUMERIC/DECIMAL does not affect appropriate underlying integer type. On contrary, changing bind of integer datatype also affects appropriate NUMERICs/DECIMALs.

Special TO part format LEGACY is used when datatype, missing in previous FB version, should be represented in a way, understandable by old client software (may be with some data losses). The following coercions are done for legacy datatypes:

Native datatype	Legacy datatype
BOOLEAN	CHAR(5)
DECFLOAT	DOUBLE PRECISION
INT128	BIGINT
TIME WITH TIME ZONE	TIME WITHOUT TIME ZONE
TIMESTAMP WITH TIME ZONE	TIMESTAMP WITHOUT TIME ZONE

Using EXTENDED in the TO part directs firebird engine to coerce to extended form of FROM datatype. Currently it works only for TIME/TIMESTAMP WITH TIME ZONE - they are coerced to EXTENDED TIME/TIMESTAMP WITH TIME ZONE appropriately.

Setting NATIVE means type will be used as if there were no previous rules for it.

Except SQL-statement there are two more ways to specify data coercion - tag isc_dpb_set_bind in DPB and DataTypeCompatibility parameter in firebird.conf & databases.conf. The later the rule is introduced (.conf->DPB->SQL) the higher priotiy it has. I.e. one can override .conf in any other way and DPB from SQL statement.

Value of clumplet with isc_dpb_set_bind tag in DPB should be specified as a set of partially formed SET BIND statements, i.e. with prefix SET BIND OF is omitted, separated by semicolons. For example:

dpb->insertString(&status, isc_dpb_set_bind, "decfloat to char; int128 to char");

DataTypeCompatibility is minor firebird version for which we want to provide some compatibility regarding data types. That compatibility may be not absolute - for example SET BIND can't care about type of particular SQL functions. The following types will be described in legacy form when DataTypeCompatibility=3.0: DECFLOAT, INT128 and TIME(STAMP) WITH TIME ZONE. When DataTypeCompatibility=2.5 in addition to this list BOOLEAN will be described as legacy type as well.

Only fields returned by database engine in regular messages are modified according to SET BIND rules. Variables returned by getting slice of an array are not affected by SET BIND statement.

SQL Samples:

SELECT CAST('123.45' AS DECFLOAT(16)) FROM RDB$DATABASE;	--native

                   CAST
=======================
                 123.45

SET BIND OF DECFLOAT TO DOUBLE PRECISION;
SELECT CAST('123.45' AS DECFLOAT(16)) FROM RDB$DATABASE;	--double

                   CAST
=======================
      123.4500000000000

SET BIND OF DECFLOAT(34) TO CHAR;
SELECT CAST('123.45' AS DECFLOAT(16)) FROM RDB$DATABASE;	--still double

                   CAST
=======================
      123.4500000000000

SELECT CAST('123.45' AS DECFLOAT(34)) FROM RDB$DATABASE;	--text

CAST
==========================================
123.45

In a case of missing ICU on client:

SELECT CURRENT_TIMESTAMP FROM RDB$DATABASE;

                                        CURRENT_TIMESTAMP
=========================================================
2020-02-21 16:26:48.0230 GMT*

SET BIND OF TIME ZONE TO EXTENDED;
SELECT CURRENT_TIMESTAMP FROM RDB$DATABASE;

                                        CURRENT_TIMESTAMP
=========================================================
2020-02-21 19:26:55.6820 +03:00

4.5 KiB Raw Blame History