作者
digoal
日期
2021-03-04
标签
PostgreSQL , trim_array
背景
https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=0a687c8f103d217ff1ca8c34a644b380d89bb0ad
```
Add trim_array() function.
This has been in the SQL spec since 2008. It's a pretty thin
wrapper around the array slice functionality, but the spec
says we should have it, so here it is.
Vik Fearing, reviewed by Dian Fay
Discussion: https://postgr.es/m/fc92ce17-9655-8ff1-c62a-4dc4c8ccd815@postgresfriends.org
```
+ <row>
+ <entry role="func_table_entry"><para role="func_signature">
+ <indexterm>
+ <primary>trim_array</primary>
+ </indexterm>
+ <function>trim_array</function> ( <parameter>array</parameter> <type>anyarray</type>, <parameter>n</parameter> <type>integer</type> )
+ <returnvalue>anyarray</returnvalue>
+ </para>
+ <para>
+ Trims an array by removing the last <parameter>n</parameter> elements.
+ If the array is multidimensional, only the first dimension is trimmed.
+ </para>
+ <para>
+ <literal>trim_array(ARRAY[1,2,3,4,5,6], 2)</literal>
+ <returnvalue>{1,2,3,4}</returnvalue>
+ </para></entry>
+ </row>
+-- trim_array
+SELECT arr, trim_array(arr, 2)
+FROM
+(VALUES ('{1,2,3,4,5,6}'::bigint[]),
+ ('{1,2}'),
+ ('[10:16]={1,2,3,4,5,6,7}'),
+ ('[-15:-10]={1,2,3,4,5,6}'),
+ ('{{1,10},{2,20},{3,30},{4,40}}')) v(arr);
+ arr | trim_array
+-------------------------------+-----------------
+ {1,2,3,4,5,6} | {1,2,3,4}
+ {1,2} | {}
+ [10:16]={1,2,3,4,5,6,7} | {1,2,3,4,5}
+ [-15:-10]={1,2,3,4,5,6} | {1,2,3,4}
+ {{1,10},{2,20},{3,30},{4,40}} | {{1,10},{2,20}}
+(5 rows)
+
+SELECT trim_array(ARRAY[1, 2, 3], -1); -- fail
+ERROR: number of elements to trim must be between 0 and 3
+SELECT trim_array(ARRAY[1, 2, 3], 10); -- fail
+ERROR: number of elements to trim must be between 0 and 3
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