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Table F.31. tablefunc Functions

normal_rand(int numvals, float8 mean, float8 stddev) returns setof float8

normal_rand produces a set of normally distributed random values (Gaussian distribution).

numvals is the number of values to be returned from the function.mean is the mean of the normal distribution of values andstddev is the standard deviation of the normal distribution of values.

For example, this call requests 1000 values with a mean of 5 and a standard deviation of 3:

test=# SELECT * FROM normal_rand(1000, 5, 3);     normal_rand----------------------     1.56556322244898     9.10040991424657     5.36957140345079   -0.369151492880995    0.283600703686639       .       .       .     4.82992125404908     9.71308014517282     2.49639286969028(1000 rows)

crosstab(text sql)crosstab(text sql, int N)

Thecrosstab function is used to produce“pivot” displays, wherein data is listed across the page rather than down. For example, we might have data like

row1    val11row1    val12row1    val13...row2    val21row2    val22row2    val23...

which we wish to display like

row1    val11   val12   val13   ...row2    val21   val22   val23   ......

Thecrosstab function takes a text parameter that is an SQL query producing raw data formatted in the first way, and produces a table formatted in the second way.

Thesql parameter is an SQL statement that produces the source set of data. This statement must return onerow_name column, onecategory column, and onevalue column.N is an obsolete parameter, ignored if supplied (formerly this had to match the number of output value columns, but now that is determined by the calling query).

For example, the provided query might produce a set something like:

 row_name    cat    value----------+-------+-------  row1      cat1    val1  row1      cat2    val2  row1      cat3    val3  row1      cat4    val4  row2      cat1    val5  row2      cat2    val6  row2      cat3    val7  row2      cat4    val8

Thecrosstab function is declared to returnsetof record, so the actual names and types of the output columns must be defined in theFROM clause of the callingSELECT statement, for example:

SELECT * FROM crosstab('...') AS ct(row_name text, category_1 text, category_2 text);

This example produces a set something like:

           <== value  columns  ==> row_name   category_1   category_2----------+------------+------------  row1        val1         val2  row2        val5         val6

TheFROM clause must define the output as onerow_name column (of the same data type as the first result column of the SQL query) followed by Nvalue columns (all of the same data type as the third result column of the SQL query). You can set up as many output value columns as you wish. The names of the output columns are up to you.

Thecrosstab function produces one output row for each consecutive group of input rows with the samerow_name value. It fills the outputvalue columns, left to right, with thevalue fields from these rows. If there are fewer rows in a group than there are outputvalue columns, the extra output columns are filled with nulls; if there are more rows, the extra input rows are skipped.

In practice the SQL query should always specifyORDER BY 1,2 to ensure that the input rows are properly ordered, that is, values with the samerow_name are brought together and correctly ordered within the row. Notice thatcrosstab itself does not pay any attention to the second column of the query result; it's just there to be ordered by, to control the order in which the third-column values appear across the page.

Here is a complete example:

CREATE TABLE ct(id SERIAL, rowid TEXT, attribute TEXT, value TEXT);INSERT INTO ct(rowid, attribute, value) VALUES('test1','att1','val1');INSERT INTO ct(rowid, attribute, value) VALUES('test1','att2','val2');INSERT INTO ct(rowid, attribute, value) VALUES('test1','att3','val3');INSERT INTO ct(rowid, attribute, value) VALUES('test1','att4','val4');INSERT INTO ct(rowid, attribute, value) VALUES('test2','att1','val5');INSERT INTO ct(rowid, attribute, value) VALUES('test2','att2','val6');INSERT INTO ct(rowid, attribute, value) VALUES('test2','att3','val7');INSERT INTO ct(rowid, attribute, value) VALUES('test2','att4','val8');SELECT *FROM crosstab(  'select rowid, attribute, value   from ct   where attribute = ''att2'' or attribute = ''att3''   order by 1,2')AS ct(row_name text, category_1 text, category_2 text, category_3 text); row_name | category_1 | category_2 | category_3----------+------------+------------+------------ test1    | val2       | val3       | test2    | val6       | val7       |(2 rows)

You can avoid always having to write out aFROM clause to define the output columns, by setting up a custom crosstab function that has the desired output row type wired into its definition. This is described in the next section. Another possibility is to embed the requiredFROM clause in a view definition.

crosstabN(text sql)

ThecrosstabN functions are examples of how to set up custom wrappers for the generalcrosstab function, so that you need not write out column names and types in the callingSELECT query. Thetablefunc module includescrosstab2,crosstab3, andcrosstab4, whose output row types are defined as

CREATE TYPE tablefunc_crosstab_N AS (    row_name TEXT,    category_1 TEXT,    category_2 TEXT,        .        .        .    category_N TEXT);

Thus, these functions can be used directly when the input query producesrow_name andvalue columns of typetext, and you want 2, 3, or 4 output values columns. In all other ways they behave exactly as described above for the generalcrosstab function.

For instance, the example given in the previous section would also work as

SELECT *FROM crosstab3(  'select rowid, attribute, value   from ct   where attribute = ''att2'' or attribute = ''att3''   order by 1,2');

These functions are provided mostly for illustration purposes. You can create your own return types and functions based on the underlyingcrosstab() function. There are two ways to do it:

crosstab(text source_sql, text category_sql)

The main limitation of the single-parameter form ofcrosstab is that it treats all values in a group alike, inserting each value into the first available column. If you want the value columns to correspond to specific categories of data, and some groups might not have data for some of the categories, that doesn't work well. The two-parameter form ofcrosstab handles this case by providing an explicit list of the categories corresponding to the output columns.

source_sql is an SQL statement that produces the source set of data. This statement must return onerow_name column, onecategory column, and onevalue column. It may also have one or more“extra” columns. Therow_name column must be first. Thecategory andvalue columns must be the last two columns, in that order. Any columns betweenrow_name andcategory are treated as“extra”. The“extra” columns are expected to be the same for all rows with the samerow_name value.

For example,source_sql might produce a set something like:

SELECT row_name, extra_col, cat, value FROM foo ORDER BY 1; row_name    extra_col   cat    value----------+------------+-----+---------  row1         extra1    cat1    val1  row1         extra1    cat2    val2  row1         extra1    cat4    val4  row2         extra2    cat1    val5  row2         extra2    cat2    val6  row2         extra2    cat3    val7  row2         extra2    cat4    val8

category_sql is an SQL statement that produces the set of categories. This statement must return only one column. It must produce at least one row, or an error will be generated. Also, it must not produce duplicate values, or an error will be generated.category_sql might be something like:

SELECT DISTINCT cat FROM foo ORDER BY 1;    cat  -------    cat1    cat2    cat3    cat4

Thecrosstab function is declared to returnsetof record, so the actual names and types of the output columns must be defined in theFROM clause of the callingSELECT statement, for example:

SELECT * FROM crosstab('...', '...')    AS ct(row_name text, extra text, cat1 text, cat2 text, cat3 text, cat4 text);

This will produce a result something like:

                  <==  value  columns   ==>row_name   extra   cat1   cat2   cat3   cat4---------+-------+------+------+------+------  row1     extra1  val1   val2          val4  row2     extra2  val5   val6   val7   val8

TheFROM clause must define the proper number of output columns of the proper data types. If there areN columns in thesource_sql query's result, the firstN-2 of them must match up with the firstN-2 output columns. The remaining output columns must have the type of the last column of thesource_sql query's result, and there must be exactly as many of them as there are rows in thecategory_sql query's result.

Thecrosstab function produces one output row for each consecutive group of input rows with the samerow_name value. The outputrow_name column, plus any“extra” columns, are copied from the first row of the group. The outputvalue columns are filled with thevalue fields from rows having matchingcategory values. If a row'scategory does not match any output of thecategory_sql query, itsvalue is ignored. Output columns whose matching category is not present in any input row of the group are filled with nulls.

In practice thesource_sql query should always specifyORDER BY 1 to ensure that values with the samerow_name are brought together. However, ordering of the categories within a group is not important. Also, it is essential to be sure that the order of thecategory_sql query's output matches the specified output column order.

Here are two complete examples:

create table sales(year int, month int, qty int);insert into sales values(2007, 1, 1000);insert into sales values(2007, 2, 1500);insert into sales values(2007, 7, 500);insert into sales values(2007, 11, 1500);insert into sales values(2007, 12, 2000);insert into sales values(2008, 1, 1000);select * from crosstab(  'select year, month, qty from sales order by 1',  'select m from generate_series(1,12) m') as (  year int,  "Jan" int,  "Feb" int,  "Mar" int,  "Apr" int,  "May" int,  "Jun" int,  "Jul" int,  "Aug" int,  "Sep" int,  "Oct" int,  "Nov" int,  "Dec" int); year | Jan  | Feb  | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov  | Dec------+------+------+-----+-----+-----+-----+-----+-----+-----+-----+------+------ 2007 | 1000 | 1500 |     |     |     |     | 500 |     |     |     | 1500 | 2000 2008 | 1000 |      |     |     |     |     |     |     |     |     |      |(2 rows)

CREATE TABLE cth(rowid text, rowdt timestamp, attribute text, val text);INSERT INTO cth VALUES('test1','01 March 2003','temperature','42');INSERT INTO cth VALUES('test1','01 March 2003','test_result','PASS');INSERT INTO cth VALUES('test1','01 March 2003','volts','2.6987');INSERT INTO cth VALUES('test2','02 March 2003','temperature','53');INSERT INTO cth VALUES('test2','02 March 2003','test_result','FAIL');INSERT INTO cth VALUES('test2','02 March 2003','test_startdate','01 March 2003');INSERT INTO cth VALUES('test2','02 March 2003','volts','3.1234');SELECT * FROM crosstab(  'SELECT rowid, rowdt, attribute, val FROM cth ORDER BY 1',  'SELECT DISTINCT attribute FROM cth ORDER BY 1')AS(       rowid text,       rowdt timestamp,       temperature int4,       test_result text,       test_startdate timestamp,       volts float8); rowid |          rowdt           | temperature | test_result |      test_startdate      | volts-------+--------------------------+-------------+-------------+--------------------------+-------- test1 | Sat Mar 01 00:00:00 2003 |          42 | PASS        |                          | 2.6987 test2 | Sun Mar 02 00:00:00 2003 |          53 | FAIL        | Sat Mar 01 00:00:00 2003 | 3.1234(2 rows)

You can create predefined functions to avoid having to write out the result column names and types in each query. See the examples in the previous section. The underlying C function for this form ofcrosstab is namedcrosstab_hash.

connectby(text relname, text keyid_fld, text parent_keyid_fld          [, text orderby_fld ], text start_with, int max_depth          [, text branch_delim ])

Theconnectby function produces a display of hierarchical data that is stored in a table. The table must have a key field that uniquely identifies rows, and a parent-key field that references the parent (if any) of each row.connectby can display the sub-tree descending from any row.

Table F.32 explains the parameters.

The key and parent-key fields can be any data type, but they must be the same type. Note that thestart_with value must be entered as a text string, regardless of the type of the key field.

Theconnectby function is declared to returnsetof record, so the actual names and types of the output columns must be defined in theFROM clause of the callingSELECT statement, for example:

SELECT * FROM connectby('connectby_tree', 'keyid', 'parent_keyid', 'pos', 'row2', 0, '~')    AS t(keyid text, parent_keyid text, level int, branch text, pos int);

The first two output columns are used for the current row's key and its parent row's key; they must match the type of the table's key field. The third output column is the depth in the tree and must be of typeinteger. If abranch_delim parameter was given, the next output column is the branch display and must be of typetext. Finally, if anorderby_fld parameter was given, the last output column is a serial number, and must be of typeinteger.

The“branch” output column shows the path of keys taken to reach the current row. The keys are separated by the specifiedbranch_delim string. If no branch display is wanted, omit both thebranch_delim parameter and the branch column in the output column list.

If the ordering of siblings of the same parent is important, include theorderby_fld parameter to specify which field to order siblings by. This field can be of any sortable data type. The output column list must include a final integer serial-number column, if and only iforderby_fld is specified.

The parameters representing table and field names are copied as-is into the SQL queries thatconnectby generates internally. Therefore, include double quotes if the names are mixed-case or contain special characters. You may also need to schema-qualify the table name.

In large tables, performance will be poor unless there is an index on the parent-key field.

It is important that thebranch_delim string not appear in any key values, elseconnectby may incorrectly report an infinite-recursion error. Note that ifbranch_delim is not provided, a default value of~ is used for recursion detection purposes.

Here is an example:

CREATE TABLE connectby_tree(keyid text, parent_keyid text, pos int);INSERT INTO connectby_tree VALUES('row1',NULL, 0);INSERT INTO connectby_tree VALUES('row2','row1', 0);INSERT INTO connectby_tree VALUES('row3','row1', 0);INSERT INTO connectby_tree VALUES('row4','row2', 1);INSERT INTO connectby_tree VALUES('row5','row2', 0);INSERT INTO connectby_tree VALUES('row6','row4', 0);INSERT INTO connectby_tree VALUES('row7','row3', 0);INSERT INTO connectby_tree VALUES('row8','row6', 0);INSERT INTO connectby_tree VALUES('row9','row5', 0);-- with branch, without orderby_fld (order of results is not guaranteed)SELECT * FROM connectby('connectby_tree', 'keyid', 'parent_keyid', 'row2', 0, '~') AS t(keyid text, parent_keyid text, level int, branch text); keyid | parent_keyid | level |       branch-------+--------------+-------+--------------------- row2  |              |     0 | row2 row4  | row2         |     1 | row2~row4 row6  | row4         |     2 | row2~row4~row6 row8  | row6         |     3 | row2~row4~row6~row8 row5  | row2         |     1 | row2~row5 row9  | row5         |     2 | row2~row5~row9(6 rows)-- without branch, without orderby_fld (order of results is not guaranteed)SELECT * FROM connectby('connectby_tree', 'keyid', 'parent_keyid', 'row2', 0) AS t(keyid text, parent_keyid text, level int); keyid | parent_keyid | level-------+--------------+------- row2  |              |     0 row4  | row2         |     1 row6  | row4         |     2 row8  | row6         |     3 row5  | row2         |     1 row9  | row5         |     2(6 rows)-- with branch, with orderby_fld (notice that row5 comes before row4)SELECT * FROM connectby('connectby_tree', 'keyid', 'parent_keyid', 'pos', 'row2', 0, '~') AS t(keyid text, parent_keyid text, level int, branch text, pos int); keyid | parent_keyid | level |       branch        | pos-------+--------------+-------+---------------------+----- row2  |              |     0 | row2                |   1 row5  | row2         |     1 | row2~row5           |   2 row9  | row5         |     2 | row2~row5~row9      |   3 row4  | row2         |     1 | row2~row4           |   4 row6  | row4         |     2 | row2~row4~row6      |   5 row8  | row6         |     3 | row2~row4~row6~row8 |   6(6 rows)-- without branch, with orderby_fld (notice that row5 comes before row4)SELECT * FROM connectby('connectby_tree', 'keyid', 'parent_keyid', 'pos', 'row2', 0) AS t(keyid text, parent_keyid text, level int, pos int); keyid | parent_keyid | level | pos-------+--------------+-------+----- row2  |              |     0 |   1 row5  | row2         |     1 |   2 row9  | row5         |     2 |   3 row4  | row2         |     1 |   4 row6  | row4         |     2 |   5 row8  | row6         |     3 |   6(6 rows)