feat: query to fetch unique columns

Signed-off-by: Muhammad Aaqil <[email protected]>

Author: aaqilniz

lib/discovery.js

@@ -335,6 +335,40 @@ function mixinDiscovery(PostgreSQL) {
     return sql;
   };
 
+  /**
+   * Discover unique keys for a given table
+   * @param {String} table The table name
+   * @param {Object} options The options for discovery
+   */
+
+  /*!
+   * Retrieves a list of column names that have unique key index
+   * @param schema
+   * @param table
+   * @returns {string}
+   */
+  PostgreSQL.prototype.buildQueryUniqueKeys = function(schema, table) {
+    const sql = `
+        SELECT
+            a.attname AS "columnName",
+            n.nspname AS "owner",
+            c.relname AS "tableName"
+        FROM pg_index i
+        JOIN pg_class c ON c.oid = i.indrelid
+        JOIN pg_namespace n ON n.oid = c.relnamespace
+        JOIN pg_attribute a ON a.attrelid = c.oid AND a.attnum = ANY(i.indkey)
+        WHERE i.indisunique = true
+        AND i.indisprimary = false
+        AND n.nspname = $1
+        AND c.relname = $2
+        ORDER BY a.attnum;
+    `;
+    return {
+        text: sql,
+        values: [schema, table]
+    };
+  };
+
   /**
    * Discover foreign keys that reference to the primary key of this table
    * @param {String} table The table name