Add functions: iif, ifnull, nullif

drift/lib/src/runtime/query_builder/expressions/expression.dart

@@ -159,6 +159,12 @@ abstract class Expression<D extends Object> implements FunctionParameter {
     return CaseWhenExpression<T>(this, when.entries.toList(), orElse);
   }
 
+  /// Evaluates to `this` if [predicate] is true, otherwise evaluates to [ifFalse].
+  Expression<T> iif<T extends Object>(
+      Expression<bool> predicate, Expression<T> ifFalse) {
+    return FunctionCallExpression<T>('IIF', [predicate, this, ifFalse]);
+  }
+
   /// Writes this expression into the [GenerationContext], assuming that there's
   /// an outer expression with [precedence]. If the [Expression.precedence] of
   /// `this` expression is lower, it will be wrap}ped in

drift/lib/src/runtime/query_builder/expressions/null_check.dart

@@ -29,6 +29,21 @@ Expression<T> coalesce<T extends Object>(List<Expression<T>> expressions) {
   return FunctionCallExpression<T>('COALESCE', expressions);
 }
 
+/// Evaluates to the first expression that's not null, or null if both evaluate
+/// to null. See [coalesce] if you need more than 2.
+Expression<T> ifNull<T extends Object>(
+    Expression<T> first, Expression<T> second) {
+  return FunctionCallExpression<T>('IFNULL', [first, second]);
+}
+
+/// Extension defines the `nullIf` members.
+extension SqlNullIf on Expression {
+  /// Returns null if both [matcher] matches this expression.
+  Expression nullIf(Expression matcher) {
+    return FunctionCallExpression('NULLIF', [this, matcher]);
+  }
+}
+
 class _NullCheck extends Expression<bool> {
   final Expression _inner;
   final bool _isNull;