From fcfdfb7458fd28ff17e02cf088a215f5f8cb059c Mon Sep 17 00:00:00 2001
From: rrrship <107106908+rrrship@users.noreply.github.com>
Date: Wed, 20 Jul 2022 00:38:40 +0300
Subject: [PATCH] add support for drop column if exists (#1594)

---
 .../statement/alter/AlterExpression.java           |  3 +++
 .../net/sf/jsqlparser/parser/JSqlParserCC.jjt      |  1 +
 .../sf/jsqlparser/statement/alter/AlterTest.java   | 14 ++++++++++++++
 3 files changed, 18 insertions(+)

diff --git a/src/main/java/net/sf/jsqlparser/statement/alter/AlterExpression.java b/src/main/java/net/sf/jsqlparser/statement/alter/AlterExpression.java
index 0e7422345..b537b4f03 100644
--- a/src/main/java/net/sf/jsqlparser/statement/alter/AlterExpression.java
+++ b/src/main/java/net/sf/jsqlparser/statement/alter/AlterExpression.java
@@ -412,6 +412,9 @@ public String toString() {
           if (hasColumn) {
             b.append("COLUMN ");
           }
+          if (usingIfExists) {
+            b.append("IF EXISTS ");
+          }
           if (operation == AlterOperation.RENAME) {
             b.append(columnOldName).append(" TO ");
           }
diff --git a/src/main/jjtree/net/sf/jsqlparser/parser/JSqlParserCC.jjt b/src/main/jjtree/net/sf/jsqlparser/parser/JSqlParserCC.jjt
index 229a16bff..a5df719b7 100644
--- a/src/main/jjtree/net/sf/jsqlparser/parser/JSqlParserCC.jjt
+++ b/src/main/jjtree/net/sf/jsqlparser/parser/JSqlParserCC.jjt
@@ -5991,6 +5991,7 @@ AlterExpression AlterExpression():
                 |
                 (
                     ( LOOKAHEAD(2) <K_COLUMN> { alterExp.hasColumn(true); } )?
+                    [<K_IF> <K_EXISTS> { alterExp.setUsingIfExists(true); } ]
                     (tk=<S_IDENTIFIER>    | tk=<S_QUOTED_IDENTIFIER>) { alterExp.setColumnName(tk.image); }
 
                     [ "INVALIDATE" { alterExp.addParameters("INVALIDATE"); } ]
diff --git a/src/test/java/net/sf/jsqlparser/statement/alter/AlterTest.java b/src/test/java/net/sf/jsqlparser/statement/alter/AlterTest.java
index f977df132..0b233ba4b 100644
--- a/src/test/java/net/sf/jsqlparser/statement/alter/AlterTest.java
+++ b/src/test/java/net/sf/jsqlparser/statement/alter/AlterTest.java
@@ -789,4 +789,18 @@ public void testAlterTableChangeColumnDropDefault() throws JSQLParserException {
         assertSqlCanBeParsedAndDeparsed("ALTER TABLE a MODIFY (COLUMN b DROP DEFAULT, COLUMN b DROP NOT NULL)", true);
     }
 
+    @Test
+    public void testAlterTableDropColumnIfExists() throws JSQLParserException {
+        assertSqlCanBeParsedAndDeparsed("ALTER TABLE test DROP COLUMN IF EXISTS name");
+    }
+
+    @Test
+    public void testAlterTableDropMultipleColumnsIfExists() throws JSQLParserException {
+        assertSqlCanBeParsedAndDeparsed("ALTER TABLE test DROP COLUMN IF EXISTS name, DROP COLUMN IF EXISTS surname");
+    }
+
+    @Test
+    public void testAlterTableDropMultipleColumnsIfExistsWithParams() throws JSQLParserException {
+        assertSqlCanBeParsedAndDeparsed("ALTER TABLE test DROP COLUMN IF EXISTS name CASCADE, DROP COLUMN IF EXISTS surname CASCADE");
+    }
 }