[#5315] Add support for ALTER TABLE .. DROP IF EXISTS

jOOQ/src/main/java/org/jooq/AlterTableStep.java

@@ -279,6 +279,33 @@ public interface AlterTableStep {
     @Support({ CUBRID, DERBY, FIREBIRD, H2, HSQLDB, MARIADB, MYSQL, POSTGRES })
     AlterTableDropStep drop(String field);
 
+    /**
+     * Add an <code>DROP COLUMN IF EXISTS</code> clause to the
+     * <code>ALTER TABLE</code> statement.
+     * <p>
+     * This is an alias for {@link #dropColumnIfExists(Field)}.
+     */
+    @Support({ H2, POSTGRES })
+    AlterTableDropStep dropIfExists(Field<?> field);
+
+    /**
+     * Add an <code>DROP COLUMN IF EXISTS</code> clause to the
+     * <code>ALTER TABLE</code> statement.
+     * <p>
+     * This is an alias for {@link #dropColumnIfExists(Name)}.
+     */
+    @Support({ H2, POSTGRES })
+    AlterTableDropStep dropIfExists(Name field);
+
+    /**
+     * Add an <code>DROP COLUMN IF EXISTS</code> clause to the
+     * <code>ALTER TABLE</code> statement.
+     * <p>
+     * This is an alias for {@link #dropColumnIfExists(String)}.
+     */
+    @Support({ H2, POSTGRES })
+    AlterTableDropStep dropIfExists(String field);
+
     /**
      * Add an <code>DROP COLUMN</code> clause to the <code>ALTER TABLE</code>
      * statement.
@@ -300,6 +327,27 @@ public interface AlterTableStep {
     @Support({ CUBRID, DERBY, FIREBIRD, H2, HSQLDB, MARIADB, MYSQL, POSTGRES })
     AlterTableDropStep dropColumn(String field);
 
+    /**
+     * Add an <code>DROP COLUMN IF EXISTS</code> clause to the <code>ALTER TABLE</code>
+     * statement.
+     */
+    @Support({ H2, POSTGRES })
+    AlterTableDropStep dropColumnIfExists(Field<?> field);
+
+    /**
+     * Add an <code>DROP COLUMN IF EXISTS</code> clause to the <code>ALTER TABLE</code>
+     * statement.
+     */
+    @Support({ H2, POSTGRES })
+    AlterTableDropStep dropColumnIfExists(Name field);
+
+    /**
+     * Add an <code>DROP COLUMN IF EXISTS</code> clause to the <code>ALTER TABLE</code>
+     * statement.
+     */
+    @Support({ H2, POSTGRES })
+    AlterTableDropStep dropColumnIfExists(String field);
+
     /**
      * Add a <code>DROP CONSTRAINT</code> clause to the <code>ALTER TABLE</code>
      * statement.

jOOQ/src/main/java/org/jooq/impl/AlterTableImpl.java

@@ -161,6 +161,7 @@ final class AlterTableImpl extends AbstractQuery implements
 
     private final Table<?>                   table;
     private final boolean                    ifExists;
+    private boolean                          ifExistsColumn;
     private Table<?>                         renameTo;
     private Field<?>                         renameColumn;
     private Field<?>                         renameColumnTo;
@@ -440,6 +441,21 @@ final class AlterTableImpl extends AbstractQuery implements
         return dropColumn(field);
     }
 
+    @Override
+    public final AlterTableImpl dropIfExists(Field<?> field) {
+        return dropColumnIfExists(field);
+    }
+
+    @Override
+    public final AlterTableImpl dropIfExists(Name field) {
+        return dropColumnIfExists(field);
+    }
+
+    @Override
+    public final AlterTableImpl dropIfExists(String field) {
+        return dropColumnIfExists(field);
+    }
+
     @Override
     public final AlterTableImpl dropColumn(Name field) {
         return dropColumn(field(field));
@@ -456,6 +472,22 @@ final class AlterTableImpl extends AbstractQuery implements
         return this;
     }
 
+    @Override
+    public final AlterTableImpl dropColumnIfExists(Name field) {
+        return dropColumnIfExists(field(field));
+    }
+
+    @Override
+    public final AlterTableImpl dropColumnIfExists(String field) {
+        return dropColumnIfExists(name(field));
+    }
+
+    @Override
+    public final AlterTableImpl dropColumnIfExists(Field<?> field) {
+        ifExistsColumn = true;
+        return dropColumn(field);
+    }
+
     @Override
     public final AlterTableImpl drop(Constraint constraint) {
         dropConstraint = constraint;
@@ -505,6 +537,19 @@ final class AlterTableImpl extends AbstractQuery implements
     }
 
     private final void accept0(Context<?> ctx) {
+        if (ifExistsColumn && !supportsIfExists(ctx)) {
+            Field<?> field = field(table.getQualifiedName().append(dropColumn.getUnqualifiedName()));
+
+            Tools.beginTryCatchIfExistsColumn(ctx, DDLStatementType.ALTER_TABLE, field);
+            accept1(ctx);
+            Tools.endTryCatchIfExistsColumn(ctx, DDLStatementType.ALTER_TABLE, field);
+        }
+        else {
+            accept1(ctx);
+        }
+    }
+
+    private final void accept1(Context<?> ctx) {
         SQLDialect family = ctx.family();
 
 
@@ -558,10 +603,10 @@ final class AlterTableImpl extends AbstractQuery implements
             }
         }
 
-        accept1(ctx);
+        accept2(ctx);
     }
 
-    private final void accept1(Context<?> ctx) {
+    private final void accept2(Context<?> ctx) {
         SQLDialect family = ctx.family();
 
         boolean omitAlterTable =
@@ -835,6 +880,21 @@ final class AlterTableImpl extends AbstractQuery implements
                     break;
             }
 
+            if (ifExistsColumn) {
+                switch (family) {
+
+
+
+
+
+                    case H2:
+                    case POSTGRES:
+                    default:
+                        ctx.sql(' ').visit(K_IF_EXISTS);
+                        break;
+                }
+            }
+
             ctx.sql(' ')
                .qualify(false)
                .visit(dropColumn)
@@ -949,7 +1009,7 @@ final class AlterTableImpl extends AbstractQuery implements
 
 
 
-        accept1(ctx);
+        accept2(ctx);
 
 
 

jOOQ/src/main/java/org/jooq/impl/Tools.java

@@ -3778,6 +3778,54 @@ final class Tools {
 
 
 
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+            default:
+                beginTryCatch(ctx, type);
+                break;
+        }
+    }
+
+    static final void beginTryCatchIfExistsColumn(Context<?> ctx, DDLStatementType type, QueryPart object) {
+        switch (ctx.family()) {
+
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@@ -3817,6 +3865,24 @@ final class Tools {
 
 
 
+            default:
+                endTryCatch(ctx, type);
+                break;
+        }
+    }
+
+    static final void endTryCatchIfExistsColumn(Context<?> ctx, DDLStatementType type, QueryPart object) {
+        switch (ctx.family()) {
+
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             default:
                 endTryCatch(ctx, type);
                 break;