From 01c5149ba243b137061b00511b56dd81fdf0a94c Mon Sep 17 00:00:00 2001
From: lukaseder <lukas.eder@gmail.com>
Date: Tue, 29 Jan 2019 11:59:24 +0100
Subject: [PATCH] [#7518] Support parsing ALTER TABLE .. DROP COLUMN IF EXISTS

---
 .../resources/org/jooq/web/grammar-3.12.txt   |  2 +-
 .../main/java/org/jooq/impl/ParserImpl.java   | 28 +++++++++++++------
 2 files changed, 20 insertions(+), 10 deletions(-)

diff --git a/jOOQ-manual/src/main/resources/org/jooq/web/grammar-3.12.txt b/jOOQ-manual/src/main/resources/org/jooq/web/grammar-3.12.txt
index fca2775b82..84172da42d 100644
--- a/jOOQ-manual/src/main/resources/org/jooq/web/grammar-3.12.txt
+++ b/jOOQ-manual/src/main/resources/org/jooq/web/grammar-3.12.txt
@@ -147,7 +147,7 @@ alterTableStatement = 'ALTER TABLE' [ 'IF EXISTS' ] tableName break
   | '(' column ')'
   )
 | 'COMMENT' [ '=' ] stringLiteral
-| 'DROP' [ 'COLUMN' ] identifier [ 'CASCADE' | 'RESTRICT' ]
+| 'DROP' [ 'COLUMN' ] [ 'IF EXISTS' ] identifier [ 'CASCADE' | 'RESTRICT' ]
 | 'DROP CONSTRAINT' constraintName
 | 'RENAME' [ ( 'COLUMN' | 'INDEX' | 'CONSTRAINT' ) identifier ] ( 'TO' | 'AS' ) identifier
 )
diff --git a/jOOQ/src/main/java/org/jooq/impl/ParserImpl.java b/jOOQ/src/main/java/org/jooq/impl/ParserImpl.java
index 45b68efff3..b77aea504c 100644
--- a/jOOQ/src/main/java/org/jooq/impl/ParserImpl.java
+++ b/jOOQ/src/main/java/org/jooq/impl/ParserImpl.java
@@ -3360,10 +3360,10 @@ final class ParserImpl implements Parser {
     }
 
     private static final DDLQuery parseAlterTable(ParserContext ctx) {
-        boolean ifExists = parseKeywordIf(ctx, "IF EXISTS");
+        boolean ifTableExists = parseKeywordIf(ctx, "IF EXISTS");
         Table<?> tableName = parseTableName(ctx);
 
-        AlterTableStep s1 = ifExists
+        AlterTableStep s1 = ifTableExists
             ? ctx.dsl.alterTableIfExists(tableName)
             : ctx.dsl.alterTable(tableName);
 
@@ -3403,17 +3403,20 @@ final class ParserImpl implements Parser {
                     }
                     else {
                         parseKeywordIf(ctx, "COLUMN");
+                        boolean ifColumnExists = parseKeywordIf(ctx, "IF EXISTS");
                         boolean parens = parseIf(ctx, '(');
                         Field<?> field = parseFieldName(ctx);
                         List<Field<?>> fields = null;
 
-                        while (parseIf(ctx, ',')) {
-                            if (fields == null) {
-                                fields = new ArrayList<Field<?>>();
-                                fields.add(field);
-                            }
+                        if (!ifColumnExists) {
+                            while (parseIf(ctx, ',')) {
+                                if (fields == null) {
+                                    fields = new ArrayList<Field<?>>();
+                                    fields.add(field);
+                                }
 
-                            fields.add(parseFieldName(ctx));
+                                fields.add(parseFieldName(ctx));
+                            }
                         }
 
                         if (parens)
@@ -3422,13 +3425,20 @@ final class ParserImpl implements Parser {
                         boolean cascade = parseKeywordIf(ctx, "CASCADE");
                         boolean restrict = !cascade && parseKeywordIf(ctx, "RESTRICT");
 
-                        AlterTableDropStep s2 = fields == null ? s1.dropColumn(field) : s1.dropColumns(fields);
+                        AlterTableDropStep s2 =
+                              fields == null
+                            ? ifColumnExists
+                                ? s1.dropColumnIfExists(field)
+                                : s1.dropColumn(field)
+                            : s1.dropColumns(fields);
+
                         AlterTableFinalStep s3 =
                               cascade
                             ? s2.cascade()
                             : restrict
                             ? s2.restrict()
                             : s2;
+
                         return s3;
                     }
                 }