implemented drop column if exists for postgres

Signed-off-by: involk-secure-1609 <[email protected]>

Author: kev1N916

src/backend/mysql/table.rs

@@ -190,8 +190,11 @@ impl TableBuilder for MysqlQueryBuilder {
                         sql.write_str(" TO ").unwrap();
                         self.prepare_iden(to_name, sql);
                     }
-                    TableAlterOption::DropColumn(column_name) => {
+                    TableAlterOption::DropColumn(DropColumnOption { column_name, if_exists }) => {
                         sql.write_str("DROP COLUMN ").unwrap();
+                        if *if_exists{
+                             panic!("MySQL does not support drop column if exists");
+                        }
                         self.prepare_iden(column_name, sql);
                     }
                     TableAlterOption::DropForeignKey(name) => {

src/backend/postgres/table.rs

@@ -170,8 +170,14 @@ impl TableBuilder for PostgresQueryBuilder {
                         sql.write_str(" TO ").unwrap();
                         self.prepare_iden(to_name, sql);
                     }
-                    TableAlterOption::DropColumn(column_name) => {
+                    TableAlterOption::DropColumn(DropColumnOption{
+                        column_name,
+                        if_exists
+                    }) => {
                         sql.write_str("DROP COLUMN ").unwrap();
+                         if *if_exists {
+                            sql.write_str("IF EXISTS ").unwrap();
+                        }
                         self.prepare_iden(column_name, sql);
                     }
                     TableAlterOption::DropForeignKey(name) => {

src/backend/sqlite/table.rs

@@ -62,9 +62,15 @@ impl TableBuilder for SqliteQueryBuilder {
                 sql.write_str(" TO ").unwrap();
                 self.prepare_iden(to_name, sql);
             }
-            TableAlterOption::DropColumn(col_name) => {
+            TableAlterOption::DropColumn(DropColumnOption {
+                column_name,
+                if_exists,
+            }) => {
                 sql.write_str("DROP COLUMN ").unwrap();
-                self.prepare_iden(col_name, sql);
+                if *if_exists {
+                    panic!("Sqlite does not support drop column if exists");
+                }
+                self.prepare_iden(column_name, sql);
             }
             TableAlterOption::DropForeignKey(_) => {
                 panic!(

src/table/alter.rs

@@ -42,6 +42,13 @@ pub struct AddColumnOption {
     pub(crate) if_not_exists: bool,
 }
 
+/// table alter drop column options
+#[derive(Debug, Clone)]
+pub struct DropColumnOption {
+    pub(crate) column_name: DynIden,
+    pub(crate) if_exists: bool,
+}
+
 /// All available table alter options
 #[allow(clippy::large_enum_variant)]
 #[derive(Debug, Clone)]
@@ -50,7 +57,7 @@ pub enum TableAlterOption {
     AddColumn(AddColumnOption),
     ModifyColumn(ColumnDef),
     RenameColumn(DynIden, DynIden),
-    DropColumn(DynIden),
+    DropColumn(DropColumnOption),
     AddForeignKey(TableForeignKey),
     DropForeignKey(DynIden),
 }
@@ -234,7 +241,38 @@ impl TableAlterStatement {
     where
         T: IntoIden,
     {
-        self.add_alter_option(TableAlterOption::DropColumn(col_name.into_iden()))
+        self.add_alter_option(TableAlterOption::DropColumn(DropColumnOption {
+            column_name: col_name.into(),
+            if_exists: false,
+        }))
+    }
+
+    /// Drop a column from an existing table if it exists
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use sea_query::{tests_cfg::*, *};
+    ///
+    /// let table = Table::alter()
+    ///     .table(Font::Table)
+    ///     .drop_column_if_exists("new_column")
+    ///     .to_owned();
+    ///
+    /// assert_eq!(
+    ///     table.to_string(PostgresQueryBuilder),
+    ///     r#"ALTER TABLE "font" DROP COLUMN IF EXISTS "new_column""#
+    /// );
+    /// // MySQL and Sqlite do not support DROP COLUMN IF EXISTS
+    /// ```
+    pub fn drop_column_if_exists<T>(&mut self, col_name: T) -> &mut Self
+    where
+        T: IntoIden,
+    {
+        self.add_alter_option(TableAlterOption::DropColumn(DropColumnOption {
+            column_name: col_name.into(),
+            if_exists: true,
+        }))
     }
 
     /// Add a foreign key to existing table