feat: query to fetch unique columns

Signed-off-by: Muhammad Aaqil <aaqilcs102@gmail.com>

lib/sql.js

@@ -2105,3 +2105,32 @@ SQLConnector.prototype.setNullableProperty = function(property) {
   throw new Error(g.f('{{setNullableProperty}} must be implemented by' +
   'the connector'));
 };
+
+/**
+ * Build sql to discover properties with unique index
+ */
+SQLConnector.prototype.buildQueryUniqueKeys = function(schema, table) {
+  throw new Error(g.f('{{buildQueryUniqueKeys}} must be implemented by the connector'));
+};
+
+/**
+ * Discover properties with unique index
+ * @param {String} table The table name
+ * @param {Object} options The options for discovery
+ * @param {Function} [cb] The callback function
+ */
+SQLConnector.prototype.discoverUniqueKeys = function(table, options, cb) {
+  const self = this;
+  const args = self.getArgs(table, options, cb);
+  let schema = args.schema || args.owner;
+
+  if (typeof (self.getDefaultSchema) === 'function' && !schema) {
+    schema = self.getDefaultSchema();
+  }
+  table = args.table;
+  options = args.options;
+  cb = args.cb;
+
+  const sql = self.buildQueryUniqueKeys(schema, table);
+  this.execute(sql, cb);
+};