diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml index 89c5d75a3b..5e95325250 100644 --- a/doc/src/sgml/func.sgml +++ b/doc/src/sgml/func.sgml @@ -11457,14 +11457,28 @@ table2-mapping - In json_populate_record, json_populate_recordset, - json_to_record and json_to_recordset, - type coercion from the JSON is best effort and may not result - in desired values for some types. JSON keys are matched to - identical column names in the target row type. JSON fields that do not - appear in the target row type will be omitted from the output, and - target columns that do not match any JSON field will simply be NULL. + While the examples for the functions + json_populate_record, + json_populate_recordset, + json_to_record and + json_to_recordset use constants, the typical use + would be to reference a table in the FROM clause + and use one of its json or jsonb columns + as an argument to the function. Extracted key values can then be + referenced in other parts of the query, like WHERE + clauses and target lists. Extracting multiple values in this + way can improve performance over extracting them separately with + per-key operators. + + + JSON keys are matched to identical column names in the target + row type. JSON type coercion for these functions is best + effort and may not result in desired values for some types. + JSON fields that do not appear in the target row type will be + omitted from the output, and target columns that do not match any + JSON field will simply be NULL. +