yii\db\mssql\Schema::findTableConstraints PHP Method

    protected function findTableConstraints($table, $type)
    {
        $keyColumnUsageTableName = 'INFORMATION_SCHEMA.KEY_COLUMN_USAGE';
        $tableConstraintsTableName = 'INFORMATION_SCHEMA.TABLE_CONSTRAINTS';
        if ($table->catalogName !== null) {
            $keyColumnUsageTableName = $table->catalogName . '.' . $keyColumnUsageTableName;
            $tableConstraintsTableName = $table->catalogName . '.' . $tableConstraintsTableName;
        }
        $keyColumnUsageTableName = $this->quoteTableName($keyColumnUsageTableName);
        $tableConstraintsTableName = $this->quoteTableName($tableConstraintsTableName);
        $sql = <<<SQL
SELECT
    [kcu].[constraint_name] AS [index_name],
    [kcu].[column_name] AS [field_name]
FROM {$keyColumnUsageTableName} AS [kcu]
LEFT JOIN {$tableConstraintsTableName} AS [tc] ON
    [kcu].[table_schema] = [tc].[table_schema] AND
    [kcu].[table_name] = [tc].[table_name] AND
    [kcu].[constraint_name] = [tc].[constraint_name]
WHERE
    [tc].[constraint_type] = :type AND
    [kcu].[table_name] = :tableName AND
    [kcu].[table_schema] = :schemaName
SQL;
        return $this->db->createCommand($sql, [':tableName' => $table->name, ':schemaName' => $table->schemaName, ':type' => $type])->queryAll();
    }