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AVG Examples

SELECT
  dept_no,
  AVG(salary)
FROM employee
GROUP BY dept_no
See also

SELECT

COUNT()

Counts non-NULL values

Result type

BIGINT

Syntax
COUNT ([ALL | DISTINCT] <expr> | *)
Table 1. COUNT Function Parameters
Parameter Description

expr

Expression.It may contain a table column, a constant, a variable, an expression, a non-aggregate function or a UDF that returns a numeric data type.Aggregate functions are not allowed as expressions

COUNT returns the number of non-null values in a group.

  • ALL is the default: it counts all values in the set that are not NULL.

  • If DISTINCT is specified, duplicates are excluded from the counted set.

  • If COUNT (*) is specified instead of the expression expr, all rows will be counted.COUNT (*) — 

    • does not accept parameters

    • cannot be used with the keyword DISTINCT

    • does not take an expr argument, since its context is column-unspecific by definition

    • counts each row separately and returns the number of rows in the specified table or group without omitting duplicate rows

    • counts rows containing NULL

  • If the result set is empty or contains only NULL in the specified column(s), the returned count is zero.

COUNT Examples

SELECT
  dept_no,
  COUNT(*) AS cnt,
  COUNT(DISTINCT name) AS cnt_name
FROM employee
GROUP BY dept_no
See also

SELECT.

LIST()

Concatenates values into a string list

Result type

BLOB

Syntax
LIST ([ALL | DISTINCT] <expr> [, separator ])
Table 1. LIST Function Parameters
Parameter Description

expr

Expression.It may contain a table column, a constant, a variable, an expression, a non-aggregate function or a UDF that returns the string data type or a BLOB.Fields of numeric and date/time types are converted to strings.Aggregate functions are not allowed as expressions.

separator

Optional alternative separator, a string expression.Comma is the default separator

LIST returns a string consisting of the non-NULL argument values in the group, separated either by a comma or by a user-supplied separator.If there are no non-NULL values (this includes the case where the group is empty), NULL is returned.

  • ALL (the default) results in all non-NULL values being listed.With DISTINCT, duplicates are removed, except if expr is a BLOB.

  • The optional separator argument may be any string expression.This makes it possible to specify e.g. ascii_char(13) as a separator.

  • The expr and separator arguments support BLOBs of any size and character set.

  • Datetime and numeric arguments are implicitly converted to strings before concatenation.

  • The result is a text BLOB, except when expr is a BLOB of another subtype.

  • The ordering of the list values is undefined — the order in which the strings are concatenated is determined by read order from the source set which, in tables, is not generally defined.If ordering is important, the source data can be pre-sorted using a derived table or similar.

    Caution

    This is a trick/workaround, and it depends on implementation details of the optimizer/execution order.This trick doesn’t always work, and it is not guaranteed to work across versions.

    Some reports indicate this no longer works in Firebird 5.0, or only in more limited circumstances than in previous versions.