MaxGekk commented on a change in pull request #33693:
URL: https://github.com/apache/spark/pull/33693#discussion_r686567577
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File path: docs/sql-ref-literals.md
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@@ -439,32 +439,93 @@ SELECT TIMESTAMP '1997-01' AS col;
An interval literal is used to specify a fixed period of time.
+#### ANSI style
+
+The ANSI SQL standard defines interval literals in the form:
+```sql
+INTERVAL [ <sign> ] <interval string> <interval qualifier>
+```
+where `<interval qualifier>` can be a single field or in the field-to-field
form:
+```sql
+<interval qualifier> ::= <start field> TO <end field> | <single field>
+```
+An interval literal can have either year-month or day-time interval type. The
interval sub-type defines format of `<interval string>`:
+```sql
+<interval string> ::= <quote> [ <sign> ] { <year-month literal> | <day-time
literal> } <quote>
+<year-month literal> ::= <years value> [ <minus sign> <months value> ] |
<months value>
+<day-time literal> ::= <day-time interval> | <time interval>
+<day-time interval> ::= <days value> [ <space> <hours value> [ <colon>
<minutes value> [ <colon> <seconds value> ] ] ]
+<time interval> ::= <hours value> [ <colon> <minutes value> [ <colon> <seconds
value> ] ]
+ | <minutes value> [ <colon> <seconds value> ]
+ | <seconds value>
+```
+
+Supported year-month interval literals and theirs formats:
Review comment:
The purpose of the table below is to demonstrate the valid combination
of fields, actually, too. Case sensitivity is not interval specific, and
applicable to other SQL statements. It is not worthy to mention it, example is
enough.
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