framework/db/mysql/Schema.php
protected function findConstraints($table)
    {
        $sql = <<<'SQL'
SELECT
    kcu.constraint_name,
    kcu.column_name,
    kcu.referenced_table_name,
    kcu.referenced_column_name
FROM information_schema.referential_constraints AS rc
JOIN information_schema.key_column_usage AS kcu ON
    (
        kcu.constraint_catalog = rc.constraint_catalog OR
        (kcu.constraint_catalog IS NULL AND rc.constraint_catalog IS NULL)
    ) AND
    kcu.constraint_schema = rc.constraint_schema AND
    kcu.constraint_name = rc.constraint_name
WHERE rc.constraint_schema = database() AND kcu.table_schema = database()
AND rc.table_name = :tableName AND kcu.table_name = :tableName1
SQL;

        try {
            $rows = $this->db->createCommand($sql, [':tableName' => $table->name, ':tableName1' => $table->name])->queryAll();
            $constraints = [];

            foreach ($rows as $row) {
                $constraints[$row['constraint_name']]['referenced_table_name'] = $row['referenced_table_name'];
                $constraints[$row['constraint_name']]['columns'][$row['column_name']] = $row['referenced_column_name'];
            }

            $table->foreignKeys = [];
            foreach ($constraints as $name => $constraint) {
                $table->foreignKeys[$name] = array_merge(
                    [$constraint['referenced_table_name']],
                    $constraint['columns']
                );
            }
        } catch (\Exception $e) {
            $previous = $e->getPrevious();
            if (!$previous instanceof \PDOException || strpos($previous->getMessage(), 'SQLSTATE[42S02') === false) {
                throw $e;
            }

            // table does not exist, try to determine the foreign keys using the table creation sql
            $sql = $this->getCreateTableSql($table);
            $regexp = '/FOREIGN KEY\s+\(([^\)]+)\)\s+REFERENCES\s+([^\(^\s]+)\s*\(([^\)]+)\)/mi';
            if (preg_match_all($regexp, $sql, $matches, PREG_SET_ORDER)) {
                foreach ($matches as $match) {
                    $fks = array_map('trim', explode(',', str_replace('`', '', $match[1])));
                    $pks = array_map('trim', explode(',', str_replace('`', '', $match[3])));
                    $constraint = [str_replace('`', '', $match[2])];
                    foreach ($fks as $k => $name) {
                        $constraint[$name] = $pks[$k];
                    }
                    $table->foreignKeys[md5(serialize($constraint))] = $constraint;
                }
                $table->foreignKeys = array_values($table->foreignKeys);
            }
        }
    }
protected function findConstraints($table)
    {
        $sql = <<<'SQL'
SELECT
    kcu.constraint_name,
    kcu.column_name,
    kcu.referenced_table_name,
    kcu.referenced_column_name
FROM information_schema.referential_constraints AS rc
JOIN information_schema.key_column_usage AS kcu ON
    (
        kcu.constraint_catalog = rc.constraint_catalog OR
        (kcu.constraint_catalog IS NULL AND rc.constraint_catalog IS NULL)
    ) AND
    kcu.constraint_schema = rc.constraint_schema AND
    kcu.constraint_name = rc.constraint_name
WHERE rc.constraint_schema = database() AND kcu.table_schema = database()
AND rc.table_name = :tableName AND kcu.table_name = :tableName1
SQL;

        try {
            $rows = $this->db->createCommand($sql, [':tableName' => $table->name, ':tableName1' => $table->name])->queryAll();
            $constraints = [];

            foreach ($rows as $row) {
                $constraints[$row['constraint_name']]['referenced_table_name'] = $row['referenced_table_name'];
                $constraints[$row['constraint_name']]['columns'][$row['column_name']] = $row['referenced_column_name'];
            }

            $table->foreignKeys = [];
            foreach ($constraints as $name => $constraint) {
                $table->foreignKeys[$name] = array_merge(
                    [$constraint['referenced_table_name']],
                    $constraint['columns']
                );
            }
        } catch (\Exception $e) {
            $previous = $e->getPrevious();
            if (!$previous instanceof \PDOException || strpos($previous->getMessage(), 'SQLSTATE[42S02') === false) {
                throw $e;
            }

            // table does not exist, try to determine the foreign keys using the table creation sql
            $sql = $this->getCreateTableSql($table);
            $regexp = '/FOREIGN KEY\s+\(([^\)]+)\)\s+REFERENCES\s+([^\(^\s]+)\s*\(([^\)]+)\)/mi';
            if (preg_match_all($regexp, $sql, $matches, PREG_SET_ORDER)) {
                foreach ($matches as $match) {
                    $fks = array_map('trim', explode(',', str_replace('`', '', $match[1])));
                    $pks = array_map('trim', explode(',', str_replace('`', '', $match[3])));
                    $constraint = [str_replace('`', '', $match[2])];
                    foreach ($fks as $k => $name) {
                        $constraint[$name] = $pks[$k];
                    }
                    $table->foreignKeys[md5(serialize($constraint))] = $constraint;
                }
                $table->foreignKeys = array_values($table->foreignKeys);
            }
        }
    }
Collects the foreign key column details for the given table.
@param TableSchema $table the table metadata
@throws \Exception