Unnesting and reforming a big query array seems to destroy null

up vote
1
down vote

favorite

SELECT ARRAY(SELECT foo FROM UNNEST(CAST(NULL as ARRAY<STRING>)) as foo) is null

returns false

vs.

SELECT CAST(NULL as ARRAY<STRING>) is null

returns true

My specific situation is that I'd like to sort an array using

SELECT ARRAY(SELECT foo from UNNEST(bar) as foo Order by foo) as arr

and keep the array as null if it was originally null. I'm open to alternatives for sorting the array but preserving null (meaning I'm not hung up on my implementation).

asked Nov 7 at 20:32

Andrew Cassidy

1,377724

add a comment |

up vote
1
down vote

favorite

SELECT ARRAY(SELECT foo FROM UNNEST(CAST(NULL as ARRAY<STRING>)) as foo) is null

returns false

vs.

SELECT CAST(NULL as ARRAY<STRING>) is null

returns true

My specific situation is that I'd like to sort an array using

SELECT ARRAY(SELECT foo from UNNEST(bar) as foo Order by foo) as arr

and keep the array as null if it was originally null. I'm open to alternatives for sorting the array but preserving null (meaning I'm not hung up on my implementation).

asked Nov 7 at 20:32

Andrew Cassidy

1,377724

add a comment |

up vote
1
down vote

favorite

SELECT ARRAY(SELECT foo FROM UNNEST(CAST(NULL as ARRAY<STRING>)) as foo) is null

returns false

vs.

SELECT CAST(NULL as ARRAY<STRING>) is null

returns true

My specific situation is that I'd like to sort an array using

SELECT ARRAY(SELECT foo from UNNEST(bar) as foo Order by foo) as arr

and keep the array as null if it was originally null. I'm open to alternatives for sorting the array but preserving null (meaning I'm not hung up on my implementation).

asked Nov 7 at 20:32

Andrew Cassidy

1,377724

SELECT ARRAY(SELECT foo FROM UNNEST(CAST(NULL as ARRAY<STRING>)) as foo) is null

returns false

vs.

SELECT CAST(NULL as ARRAY<STRING>) is null

returns true

My specific situation is that I'd like to sort an array using

SELECT ARRAY(SELECT foo from UNNEST(bar) as foo Order by foo) as arr

and keep the array as null if it was originally null. I'm open to alternatives for sorting the array but preserving null (meaning I'm not hung up on my implementation).

sql google-bigquery

asked Nov 7 at 20:32

Andrew Cassidy

1,377724

asked Nov 7 at 20:32

Andrew Cassidy

1,377724

asked Nov 7 at 20:32

Andrew Cassidy

1,377724

asked Nov 7 at 20:32

Andrew Cassidy

1,377724

asked Nov 7 at 20:32

Andrew Cassidy

1,377724

add a comment |

1 Answer
1

active

oldest

votes

up vote
2
down vote

accepted

An empty array is different from a NULL with an array type. An empty array is an array with no elements. That is what you get from the UNNEST(). So, the comparison to NULL is false.

The second is returning NULL typed as an array. This is equivalent to NULL, so the comparison is true.

answered Nov 7 at 21:05

Gordon Linoff

746k33285390

Got it. I'm used to a world where any operation on a NULL would result in a NULL....
– Andrew Cassidy
Nov 7 at 21:16

This is still true. But an array with a null element is not itself null.
– Elliott Brossard
Nov 7 at 22:30

@ElliottBrossard . . . Arrays in BQ do not have NULL elements. An empty array is not NULL.
– Gordon Linoff
Nov 7 at 22:32

Yes, that's right. I was trying to explain to the OP that operations can involve nulls (e.g. ARRAY_LENGTH applied to an array with a null element) but not result in null.
– Elliott Brossard
Nov 7 at 23:03

add a comment |

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1 Answer
1

active

oldest

votes

1 Answer
1

active

oldest

votes

up vote
2
down vote

accepted

An empty array is different from a NULL with an array type. An empty array is an array with no elements. That is what you get from the UNNEST(). So, the comparison to NULL is false.

The second is returning NULL typed as an array. This is equivalent to NULL, so the comparison is true.

answered Nov 7 at 21:05

Gordon Linoff

746k33285390

Got it. I'm used to a world where any operation on a NULL would result in a NULL....
– Andrew Cassidy
Nov 7 at 21:16

This is still true. But an array with a null element is not itself null.
– Elliott Brossard
Nov 7 at 22:30

@ElliottBrossard . . . Arrays in BQ do not have NULL elements. An empty array is not NULL.
– Gordon Linoff
Nov 7 at 22:32

Yes, that's right. I was trying to explain to the OP that operations can involve nulls (e.g. ARRAY_LENGTH applied to an array with a null element) but not result in null.
– Elliott Brossard
Nov 7 at 23:03

add a comment |

up vote
2
down vote

accepted

An empty array is different from a NULL with an array type. An empty array is an array with no elements. That is what you get from the UNNEST(). So, the comparison to NULL is false.

The second is returning NULL typed as an array. This is equivalent to NULL, so the comparison is true.

answered Nov 7 at 21:05

Gordon Linoff

746k33285390

Got it. I'm used to a world where any operation on a NULL would result in a NULL....
– Andrew Cassidy
Nov 7 at 21:16

This is still true. But an array with a null element is not itself null.
– Elliott Brossard
Nov 7 at 22:30

@ElliottBrossard . . . Arrays in BQ do not have NULL elements. An empty array is not NULL.
– Gordon Linoff
Nov 7 at 22:32

Yes, that's right. I was trying to explain to the OP that operations can involve nulls (e.g. ARRAY_LENGTH applied to an array with a null element) but not result in null.
– Elliott Brossard
Nov 7 at 23:03

add a comment |

up vote
2
down vote

accepted

An empty array is different from a NULL with an array type. An empty array is an array with no elements. That is what you get from the UNNEST(). So, the comparison to NULL is false.

The second is returning NULL typed as an array. This is equivalent to NULL, so the comparison is true.

answered Nov 7 at 21:05

Gordon Linoff

746k33285390

An empty array is different from a NULL with an array type. An empty array is an array with no elements. That is what you get from the UNNEST(). So, the comparison to NULL is false.

The second is returning NULL typed as an array. This is equivalent to NULL, so the comparison is true.

answered Nov 7 at 21:05

Gordon Linoff

746k33285390

answered Nov 7 at 21:05

Gordon Linoff

746k33285390

answered Nov 7 at 21:05

Gordon Linoff

746k33285390

answered Nov 7 at 21:05

Gordon Linoff

746k33285390

Got it. I'm used to a world where any operation on a NULL would result in a NULL....
– Andrew Cassidy
Nov 7 at 21:16

This is still true. But an array with a null element is not itself null.
– Elliott Brossard
Nov 7 at 22:30

@ElliottBrossard . . . Arrays in BQ do not have NULL elements. An empty array is not NULL.
– Gordon Linoff
Nov 7 at 22:32

Yes, that's right. I was trying to explain to the OP that operations can involve nulls (e.g. ARRAY_LENGTH applied to an array with a null element) but not result in null.
– Elliott Brossard
Nov 7 at 23:03

add a comment |

Got it. I'm used to a world where any operation on a NULL would result in a NULL....
– Andrew Cassidy
Nov 7 at 21:16

This is still true. But an array with a null element is not itself null.
– Elliott Brossard
Nov 7 at 22:30

@ElliottBrossard . . . Arrays in BQ do not have NULL elements. An empty array is not NULL.
– Gordon Linoff
Nov 7 at 22:32

Yes, that's right. I was trying to explain to the OP that operations can involve nulls (e.g. ARRAY_LENGTH applied to an array with a null element) but not result in null.
– Elliott Brossard
Nov 7 at 23:03

Got it. I'm used to a world where any operation on a NULL would result in a NULL....
– Andrew Cassidy
Nov 7 at 21:16

This is still true. But an array with a null element is not itself null.
– Elliott Brossard
Nov 7 at 22:30

@ElliottBrossard . . . Arrays in BQ do not have NULL elements. An empty array is not NULL.
– Gordon Linoff
Nov 7 at 22:32

Yes, that's right. I was trying to explain to the OP that operations can involve nulls (e.g. ARRAY_LENGTH applied to an array with a null element) but not result in null.
– Elliott Brossard
Nov 7 at 23:03

add a comment |

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