diff --git a/lib/data-types.ts b/lib/data-types.ts
index f2df9e4..59e43ab 100644
--- a/lib/data-types.ts
+++ b/lib/data-types.ts
@@ -1,5 +1,13 @@
 import { Fields } from "./query-builder.ts";
 
+export type FieldTypes =
+  | "INTEGER"
+  | "FLOAT"
+  | "BOOLEAN"
+  | "STRING"
+  | "TEXT"
+  | "DATETIME";
+
 /** Available fields data types. */
 export const DATA_TYPES: Fields = {
   INTEGER: "integer",
diff --git a/lib/query-builder.ts b/lib/query-builder.ts
index 0a28f9c..f415802 100644
--- a/lib/query-builder.ts
+++ b/lib/query-builder.ts
@@ -1,5 +1,6 @@
 import { SQLQueryBuilder } from "../deps.ts";
 import { DatabaseDialect } from "./database.ts";
+import { FieldTypes } from "./data-types.ts";
 
 export type FieldValue = number | string | boolean | Date;
 export type FieldTypeString =
@@ -9,7 +10,9 @@ export type FieldTypeString =
   | "text"
   | "date"
   | "float";
-export type Fields = { [key: string]: FieldTypeString };
+export type Fields = {
+  [key in FieldTypes]: FieldTypeString;
+};
 export type Values = { [key: string]: FieldValue };
 export type FieldType = FieldTypeString | {
   type?: FieldTypeString;