feat: update alter and drop statements (#94)

* feat: add UNIQUE keyword

* feat: support ifExist, addConstraint, dropConstraint and addUnique of alter table statement

* feat: support ifExist, addConstraint, dropConstraint and addUnique of alter table statement

* tests: add tests of alter statements

* docs: add comments for sql syntax

* build: optimize promote of build/antlr4

* ci: add max_old_space_size

* ci: add max_old_space_size

* ci: update tests script

src/grammar/flinksql/FlinkSqlParser.g4

@@ -277,19 +277,37 @@ jarFileName
     ;
 
 // Alter statements
+// Just for simple alter table statements, 
+// it only includes rename, set key, add constraint, drop constraint, add unique
 
 alterTable
-    : ALTER TABLE uid (renameDefinition | setKeyValueDefinition)
+    : ALTER TABLE ifExists? uid (renameDefinition | setKeyValueDefinition | addConstraint | dropConstraint | addUnique)
     ;
 
 renameDefinition
-    : RENAME TO uid
+    : RENAME uid? TO uid
     ;
 
 setKeyValueDefinition
     : SET tablePropertyList
     ;
 
+addConstraint
+    : ADD CONSTRAINT constraintName PRIMARY KEY columnNameList notForced?
+    ;
+
+dropConstraint
+    : DROP CONSTRAINT constraintName
+    ;
+
+addUnique
+    : ADD UNIQUE columnNameList
+    ;
+
+notForced
+    : NOT ENFORCED
+    ;
+
 alertView
     : ALTER VIEW uid (renameDefinition | AS queryStatement)
     ;