GoogleSQL for Bigtable supports the following debugging functions.

Function list

IFERROR

IFERROR(try_expression,catch_expression)

Description

Evaluatestry_expression.

Whentry_expression is evaluated:

• If the evaluation oftry_expression doesn't produce an error, thenIFERROR returns the result oftry_expression without evaluatingcatch_expression.
• If the evaluation oftry_expression produces a system error, thenIFERRORproduces that system error.
• If the evaluation oftry_expression produces an evaluation error, thenIFERROR suppresses that evaluation error and evaluatescatch_expression.

Ifcatch_expression is evaluated:

• If the evaluation ofcatch_expression doesn't produce an error, thenIFERROR returns the result ofcatch_expression.
• If the evaluation ofcatch_expression produces any error, thenIFERRORproduces that error.

Arguments

• try_expression: An expression that returns a scalar value.
• catch_expression: An expression that returns a scalar value.

The results oftry_expression andcatch_expression must share asupertype.

Return Data Type

Thesupertype fortry_expression andcatch_expression.

Example

In the following example, the query successfully evaluatestry_expression.

SELECTIFERROR('a','b')ASresult/*--------+ | result | +--------+ | a      | +--------*/

In the following example,IFERROR catches an evaluation error in thetry_expression and successfully evaluatescatch_expression.

SELECTIFERROR(ERROR('a'),'b')ASresult/*--------+ | result | +--------+ | b      | +--------*/

In the following query, the error is handled by the innermostIFERRORoperation,IFERROR(ERROR('a'), 'b').

SELECTIFERROR(IFERROR(ERROR('a'),'b'),'c')ASresult/*--------+ | result | +--------+ | b      | +--------*/

In the following query, the error is handled by the outermostIFERRORoperation,IFERROR(..., 'c').

SELECTIFERROR(IFERROR(ERROR('a'),ERROR('b')),'c')ASresult/*--------+ | result | +--------+ | c      | +--------*/

In the following example,IFERROR catches an evaluation error inERROR('a')and then evaluatesERROR('b'). Because there is also an evaluation error inERROR('b'),IFERROR produces an evaluation error forERROR('b').

SELECTIFERROR(ERROR('a'),ERROR('b'))ASresult--ERROR:OUT_OF_RANGE'b'

ISERROR

ISERROR(try_expression)

Description

Evaluatestry_expression.

• If the evaluation oftry_expression doesn't produce an error, thenISERROR returnsFALSE.
• If the evaluation oftry_expression produces a system error, thenISERRORproduces that system error.
• If the evaluation oftry_expression produces an evaluation error, thenISERROR returnsTRUE.

Arguments

• try_expression: An expression that returns a scalar value.

Return Data Type

BOOL

Example

In the following examples,ISERROR successfully evaluatestry_expression.

SELECTISERROR('a')ASis_error/*----------+ | is_error | +----------+ | false    | +----------*/

SELECTISERROR(2/1)ASis_error/*----------+ | is_error | +----------+ | false    | +----------*/

In the following examples,ISERROR catches an evaluation error intry_expression.

SELECTISERROR(ERROR('a'))ASis_error/*----------+ | is_error | +----------+ | true     | +----------*/

SELECTISERROR(2/0)ASis_error/*----------+ | is_error | +----------+ | true     | +----------*/

NULLIFERROR

NULLIFERROR(try_expression)

Description

Evaluatestry_expression.

• If the evaluation oftry_expression doesn't produce an error, thenNULLIFERROR returns the result oftry_expression.

• If the evaluation oftry_expression produces a system error, thenNULLIFERROR produces that system error.

• If the evaluation oftry_expression produces an evaluation error, thenNULLIFERROR returnsNULL.

Arguments

• try_expression: An expression that returns a scalar value.

Return Data Type

The data type fortry_expression orNULL

Example

In the following example,NULLIFERROR successfully evaluatestry_expression.

SELECTNULLIFERROR('a')ASresult/*--------+ | result | +--------+ | a      | +--------*/

In the following example,NULLIFERROR catches an evaluation error intry_expression.

SELECTNULLIFERROR(ERROR('a'))ASresult/*--------+ | result | +--------+ | NULL   | +--------*/