PostgreSQL 8.4.12 Documentation
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# 9.17. Array Functions and Operators

Table 9-40 shows the operators available for array types.

Table 9-40. Array Operators

Operator | Description | Example | Result
--- | --- | --- | ---
`=` | equal | `ARRAY[1.1,2.1,3.1]::int[] = ARRAY[1,2,3]` | `t`
`<>` | not equal | `ARRAY[1,2,3] <> ARRAY[1,2,4]` | `t`
`<` | less than | `ARRAY[1,2,3] < ARRAY[1,2,4]` | `t`
`>` | greater than | `ARRAY[1,4,3] > ARRAY[1,2,4]` | `t`
`<=` | less than or equal | `ARRAY[1,2,3] <= ARRAY[1,2,3]` | `t`
`>=` | greater than or equal | `ARRAY[1,4,3] >= ARRAY[1,4,3]` | `t`
`@>` | contains | `ARRAY[1,4,3] @> ARRAY[3,1]` | `t`
`<@` | is contained by | `ARRAY[2,7] <@ ARRAY[1,7,4,2,6]` | `t`
`&&` | overlap (have elements in common) | `ARRAY[1,4,3] && ARRAY[2,1]` | `t`
`||` | array-to-array concatenation | `ARRAY[1,2,3] || ARRAY[4,5,6]` | `{1,2,3,4,5,6}`
`||` | array-to-array concatenation | `ARRAY[1,2,3] || ARRAY[[4,5,6],[7,8,9]]` | `{{1,2,3},{4,5,6},{7,8,9}}`
`||` | element-to-array concatenation | `3 || ARRAY[4,5,6]` | `{3,4,5,6}`
`||` | array-to-element concatenation | `ARRAY[4,5,6] || 7` | `{4,5,6,7}`

Array comparisons compare the array contents element-by-element, using the default B-Tree comparison function for the element data type. In multidimensional arrays the elements are visited in row-major order (last subscript varies most rapidly). If the contents of two arrays are equal but the dimensionality is different, the first difference in the dimensionality information determines the sort order. (This is a change from versions of PostgreSQL prior to 8.2: older versions would claim that two arrays with the same contents were equal, even if the number of dimensions or subscript ranges were different.)

See Section 8.14 for more details about array operator behavior.

Table 9-41 shows the functions available for use with array types. See Section 8.14 for more information and examples of the use of these functions.

Table 9-41. Array Functions

Function | Return Type | Description | Example | Result
--- | --- | --- | --- | ---
``array_append`(`anyarray`, `anyelement`)` | `anyarray` | append an element to the end of an array | `array_append(ARRAY[1,2], 3)` | `{1,2,3}`
``array_cat`(`anyarray`, `anyarray`)` | `anyarray` | concatenate two arrays | `array_cat(ARRAY[1,2,3], ARRAY[4,5])` | `{1,2,3,4,5}`
``array_ndims`(`anyarray`)` | `int` | returns the number of dimensions of the array | `array_ndims(ARRAY[[1,2,3], [4,5,6]])` | `2`
``array_dims`(`anyarray`)` | `text` | returns a text representation of array's dimensions | `array_dims(ARRAY[[1,2,3], [4,5,6]])` | `[1:2][1:3]`
``array_fill`(`anyelement`, `int[]`, [, `int[]`])` | `anyarray` | returns an array initialized with supplied value and dimensions, optionally with lower bounds other than 1 | `array_fill(7, ARRAY[3], ARRAY[2])` | `[2:4]={7,7,7}`
``array_length`(`anyarray`, `int`)` | `int` | returns the length of the requested array dimension | `array_length(array[1,2,3], 1)` | `3`
``array_lower`(`anyarray`, `int`)` | `int` | returns lower bound of the requested array dimension | `array_lower('[0:2]={1,2,3}'::int[], 1)` | `0`
``array_prepend`(`anyelement`, `anyarray`)` | `anyarray` | append an element to the beginning of an array | `array_prepend(1, ARRAY[2,3])` | `{1,2,3}`
``array_to_string`(`anyarray`, `text`)` | `text` | concatenates array elements using supplied delimiter | `array_to_string(ARRAY[1, 2, 3], '~^~')` | `1~^~2~^~3`
``array_upper`(`anyarray`, `int`)` | `int` | returns upper bound of the requested array dimension | `array_upper(ARRAY[1,2,3,4], 1)` | `4`
``string_to_array`(`text`, `text`)` | `text[]` | splits string into array elements using supplied delimiter | `string_to_array('xx~^~yy~^~zz', '~^~')` | `{xx,yy,zz}`
``unnest`(`anyarray`)` | `setof anyelement` | expand an array to a set of rows | `unnest(ARRAY[1,2])` | `1` `2` (2 rows)

See also Section 9.18 about the aggregate function `array_agg` for use with arrays.

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