[FLINK-14980][docs] add function ddl docs

this closes apache#10732.

docs/dev/table/sql/alter.md

@@ -31,6 +31,7 @@ Flink SQL supports the following ALTER statements for now:
 
 - ALTER TABLE
 - ALTER DATABASE
+- ALTER FUNCTION
 
 ## Run an ALTER statement
 
@@ -134,4 +135,27 @@ Set one or more properties in the specified table. If a particular property is a
 ALTER DATABASE [catalog_name.]db_name SET (key1=val1, key2=val2, ...)
 {% endhighlight %}
 
-Set one or more properties in the specified database. If a particular property is already set in the database, override the old value with the new one.
+Set one or more properties in the specified database. If a particular property is already set in the database, override the old value with the new one.
+
+## ALTER FUNCTION
+
+{% highlight sql%}
+ALTER [TEMPORARY|TEMPORARY SYSTEM] FUNCTION 
+  [IF EXISTS] [catalog_name.][db_name.]function_name 
+  AS identifier [LANGUAGE JAVA|SCALA|
+{% endhighlight %}
+
+Alter a catalog function with the new identifier which is full classpath for JAVA/SCALA and optional language tag. If a function doesn't exist in the catalog, an exception is thrown.
+
+**TEMPORARY**
+Alter temporary catalog function that has catalog and database namespaces and overrides catalog functions.
+
+**TEMPORARY SYSTEM**
+Alter temporary system function that has no namespace and overrides built-in functions
+
+**IF EXISTS**
+If the function doesn't exist, nothing happens.
+
+**LANGUAGE JAVA|SCALA**
+Language tag to instruct flink runtime how to execute the function. Currently only JAVA and SCALA are supported, the default language for a function is JAVA.
+

docs/dev/table/sql/alter.zh.md

@@ -31,6 +31,7 @@ Flink SQL supports the following ALTER statements for now:
 
 - ALTER TABLE
 - ALTER DATABASE
+- ALTER FUNCTION
 
 ## Run an ALTER statement
 
@@ -134,4 +135,27 @@ Set one or more properties in the specified table. If a particular property is a
 ALTER DATABASE [catalog_name.]db_name SET (key1=val1, key2=val2, ...)
 {% endhighlight %}
 
-Set one or more properties in the specified database. If a particular property is already set in the database, override the old value with the new one.
+Set one or more properties in the specified database. If a particular property is already set in the database, override the old value with the new one.
+
+## ALTER FUNCTION
+
+{% highlight sql%}
+ALTER [TEMPORARY|TEMPORARY SYSTEM] FUNCTION 
+  [IF EXISTS] [catalog_name.][db_name.]function_name 
+  AS identifier [LANGUAGE JAVA|SCALA|
+{% endhighlight %}
+
+Alter a catalog function that has catalog and database namespaces with the new identifier which is full classpath for JAVA/SCALA and optional language tag. If a function doesn't exist in the catalog, an exception is thrown.
+
+**TEMPORARY**
+Alter temporary catalog function that has catalog and database namespaces and overrides catalog functions.
+
+**TEMPORARY SYSTEM**
+Alter temporary system function that has no namespace and overrides built-in functions
+
+**IF EXISTS**
+If the function doesn't exist, nothing happens.
+
+**LANGUAGE JAVA|SCALA**
+Language tag to instruct flink runtime how to execute the function. Currently only JAVA and SCALA are supported, the default language for a function is JAVA.
+

docs/dev/table/sql/create.md

@@ -31,6 +31,7 @@ Flink SQL supports the following CREATE statements for now:
 
 - CREATE TABLE
 - CREATE DATABASE
+- CREATE FUNCTION
 
 ## Run a CREATE statement
 
@@ -225,3 +226,24 @@ Database properties used to store extra information related to this database.
 The key and value of expression `key1=val1` should both be string literal.
 
 {% top %}
+
+## CREATE FUNCTION
+{% highlight sql%}
+CREATE [TEMPORARY|TEMPORARY SYSTEM] FUNCTION 
+  [IF NOT EXISTS] [catalog_name.][db_name.]function_name 
+  AS identifier [LANGUAGE JAVA|SCALA]
+{% endhighlight %}
+
+Create a catalog function that has catalog and database namespaces with the identifier which is full classpath for JAVA/SCALA and optional language tag. If a function with the same name already exists in the catalog, an exception is thrown.
+
+**TEMPORARY**
+Create temporary catalog function that has catalog and database namespaces and overrides catalog functions.
+
+**TEMPORARY SYSTEM**
+Create temporary system function that has no namespace and overrides built-in functions
+
+**IF NOT EXISTS**
+If the function already exists, nothing happens.
+
+**LANGUAGE JAVA|SCALA**
+Language tag to instruct flink runtime how to execute the function. Currently only JAVA and SCALA are supported, the default language for a function is JAVA.

docs/dev/table/sql/create.zh.md

@@ -31,6 +31,7 @@ Flink SQL supports the following CREATE statements for now:
 
 - CREATE TABLE
 - CREATE DATABASE
+- CREATE FUNCTION
 
 ## Run a CREATE statement
 
@@ -225,3 +226,25 @@ Database properties used to store extra information related to this database.
 The key and value of expression `key1=val1` should both be string literal.
 
 {% top %}
+
+## CREATE FUNCTION
+{% highlight sql%}
+CREATE [TEMPORARY|TEMPORARY SYSTEM] FUNCTION 
+  [IF NOT EXISTS] [[catalog_name.]db_name.]function_name 
+  AS identifier [LANGUAGE JAVA|SCALA]
+{% endhighlight %}
+
+Create a catalog function that has catalog and database namespaces with the identifier which is full classpath for JAVA/SCALA and optional language tag. If a function with the same name already exists in the catalog, an exception is thrown.
+
+**TEMPORARY**
+Create temporary catalog function that has catalog and database namespaces and overrides catalog functions.
+
+**TEMPORARY SYSTEM**
+Create temporary system function that has no namespace and overrides built-in functions
+
+**IF NOT EXISTS**
+If the function already exists, nothing happens.
+
+**LANGUAGE JAVA|SCALA**
+Language tag to instruct flink runtime how to execute the function. Currently only JAVA and SCALA are supported, the default language for a function is JAVA.
+

docs/dev/table/sql/drop.md

@@ -31,6 +31,7 @@ Flink SQL supports the following DROP statements for now:
 
 - DROP TABLE
 - DROP DATABASE
+- DROP FUNCTION
 
 ## Run a DROP statement
 
@@ -140,4 +141,21 @@ Dropping a non-empty database triggers an exception. Enabled by default.
 
 **CASCADE**
 
-Dropping a non-empty database also drops all associated tables and functions.
+Dropping a non-empty database also drops all associated tables and functions.
+
+## DROP FUNCTION
+
+{% highlight sql%}
+DROP [TEMPORARY|TEMPORARY SYSTEM] FUNCTION [IF EXISTS] [catalog_name.][db_name.]function_name;
+{% endhighlight %}
+
+Drop a catalog function that has catalog and database namespaces. If the function to drop does not exist, an exception is thrown.
+
+**TEMPORARY**
+Drop temporary catalog function that has catalog and database namespaces.
+
+**TEMPORARY SYSTEM**
+Drop temporary system function that has no namespace.
+
+**IF EXISTS**
+If the function doesn't exists, nothing happens.

docs/dev/table/sql/drop.zh.md

@@ -140,4 +140,21 @@ Dropping a non-empty database triggers an exception. Enabled by default.
 
 **CASCADE**
 
-Dropping a non-empty database also drops all associated tables and functions.
+Dropping a non-empty database also drops all associated tables and functions.
+
+## DROP FUNCTION
+
+{% highlight sql%}
+DROP [TEMPORARY|TEMPORARY SYSTEM] FUNCTION [IF EXISTS] [catalog_name.][db_name.]function_name;
+{% endhighlight %}
+
+Drop a catalog function that has catalog and database namespaces. If the function to drop does not exist, an exception is thrown.
+
+**TEMPORARY**
+Drop temporary catalog function that has catalog and database namespaces.
+
+**TEMPORARY SYSTEM**
+Drop temporary system function that has no namespace.
+
+**IF EXISTS**
+If the function doesn't exists, nothing happens.