Add example

Author: tyt2y3

src/expr.rs

@@ -267,6 +267,29 @@ impl Expr {
     ///     r#"SELECT "character", "size_w", "size_h" FROM "character" WHERE IFNULL("size_w", 0) > 2"#
     /// );
     /// ```
+    ///
+    /// ```
+    /// use sea_query::{tests_cfg::*, *};
+    ///
+    /// let query = Query::select()
+    ///     .column(Char::Character)
+    ///     .from(Char::Table)
+    ///     .and_where(Expr::expr(Func::lower(Expr::col(Char::Character))).is_in(["a", "b"]))
+    ///     .to_owned();
+    ///
+    /// assert_eq!(
+    ///     query.to_string(MysqlQueryBuilder),
+    ///     r#"SELECT `character` FROM `character` WHERE LOWER(`character`) IN ('a', 'b')"#
+    /// );
+    /// assert_eq!(
+    ///     query.to_string(PostgresQueryBuilder),
+    ///     r#"SELECT "character" FROM "character" WHERE LOWER("character") IN ('a', 'b')"#
+    /// );
+    /// assert_eq!(
+    ///     query.to_string(SqliteQueryBuilder),
+    ///     r#"SELECT "character" FROM "character" WHERE LOWER("character") IN ('a', 'b')"#
+    /// );
+    /// ```
     #[allow(clippy::self_named_constructors)]
     pub fn expr<T>(expr: T) -> Self
     where