[CALCITE-6483] Enable LEN and LENGTH in the correct function libraries

Enabled the LEN function for:
* Amazon Redshift
* Snowflake
* Spark

Enabled the LENGTH function for:
* BigQuery
* Hive
* PostgreSQL
* Amazon Redshift
* Snowflake
* Spark

core/src/main/java/org/apache/calcite/sql/fun/SqlLibraryOperators.java

@@ -287,12 +287,12 @@ private static SqlCall transformConvert(SqlValidator validator, SqlCall call) {
   public static final SqlFunction IFNULL = NVL.withName("IFNULL");
 
   /** The "LEN(string)" function. */
-  @LibraryOperator(libraries = {SNOWFLAKE, SPARK})
+  @LibraryOperator(libraries = {REDSHIFT, SNOWFLAKE, SPARK})
   public static final SqlFunction LEN =
       SqlStdOperatorTable.CHAR_LENGTH.withName("LEN");
 
   /** The "LENGTH(string)" function. */
-  @LibraryOperator(libraries = {BIG_QUERY, SNOWFLAKE, SPARK})
+  @LibraryOperator(libraries = {BIG_QUERY, HIVE, POSTGRESQL, SNOWFLAKE, SPARK})
   public static final SqlFunction LENGTH =
       SqlStdOperatorTable.CHAR_LENGTH.withName("LENGTH");
 

site/_docs/reference.md

@@ -2804,8 +2804,8 @@ In the following:
 | m | JSON_STORAGE_SIZE(jsonValue)                   | Returns the number of bytes used to store the binary representation of *jsonValue*
 | b o p r s | LEAST(expr [, expr ]* )                | Returns the least of the expressions
 | b m p r s | LEFT(string, length)                   | Returns the leftmost *length* characters from the *string*
-| f s | LEN(string)                                  | Equivalent to `CHAR_LENGTH(string)`
-| b f s | LENGTH(string)                             | Equivalent to `CHAR_LENGTH(string)`
+| f r s | LEN(string)                                | Equivalent to `CHAR_LENGTH(string)`
+| b f h p r s | LENGTH(string)                       | Equivalent to `CHAR_LENGTH(string)`
 | h s | LEVENSHTEIN(string1, string2)                | Returns the Levenshtein distance between *string1* and *string2*
 | b | LOG(numeric1 [, base ])                        | Returns the logarithm of *numeric1* to base *base*, or base e if *base* is not present, or error if *numeric1* is 0 or negative
 | m s | LOG([, base ], numeric1)                     | Returns the logarithm of *numeric1* to base *base*, or base e if *base* is not present, or null if *numeric1* is 0 or negative