diff --git a/framework/yii/db/Schema.php b/framework/yii/db/Schema.php
index f2ae94c..46288a2 100644
--- a/framework/yii/db/Schema.php
+++ b/framework/yii/db/Schema.php
@@ -248,6 +248,28 @@ abstract class Schema extends Object
 	}
 
 	/**
+	 * Returns all unique indexes for the given table.
+	 * Each array element is of the following structure:
+	 *
+	 * ~~~
+	 * [
+	 *	 'IndexName1' => ['col1' [, ...]],
+	 *	 'IndexName2' => ['col2' [, ...]],
+	 * ]
+	 * ~~~
+	 *
+	 * This method should be overridden by child classes in order to support this feature
+	 * because the default implementation simply throws an exception
+	 * @param TableSchema $table the table metadata
+	 * @return array all unique indexes for the given table.
+	 * @throws NotSupportedException if this method is called
+	 */
+	public function findUniqueIndexes($schema = '')
+	{
+		throw new NotSupportedException(get_class($this) . ' does not support getting unique indexes information.');
+	}
+
+	/**
 	 * Returns the ID of the last inserted row or sequence value.
 	 * @param string $sequenceName name of the sequence object (required by some DBMS)
 	 * @return string the row ID of the last row inserted, or the last value retrieved from the sequence object
diff --git a/framework/yii/db/mysql/Schema.php b/framework/yii/db/mysql/Schema.php
index f55d38f..075389e 100644
--- a/framework/yii/db/mysql/Schema.php
+++ b/framework/yii/db/mysql/Schema.php
@@ -207,10 +207,11 @@ class Schema extends \yii\db\Schema
 	}
 
 	/**
-	 * Collects the foreign key column details for the given table.
+	 * Gets the CREATE TABLE sql string.
 	 * @param TableSchema $table the table metadata
+	 * @return string $sql the result of 'SHOW CREATE TABLE'
 	 */
-	protected function findConstraints($table)
+	protected function getCreateTableSql($table)
 	{
 		$row = $this->db->createCommand('SHOW CREATE TABLE ' . $this->quoteSimpleTableName($table->name))->queryOne();
 		if (isset($row['Create Table'])) {
@@ -219,6 +220,16 @@ class Schema extends \yii\db\Schema
 			$row = array_values($row);
 			$sql = $row[1];
 		}
+		return $sql;
+	}
+
+	/**
+	 * Collects the foreign key column details for the given table.
+	 * @param TableSchema $table the table metadata
+	 */
+	protected function findConstraints($table)
+	{
+		$sql = $this->getCreateTableSql($table);
 
 		$regexp = '/FOREIGN KEY\s+\(([^\)]+)\)\s+REFERENCES\s+([^\(^\s]+)\s*\(([^\)]+)\)/mi';
 		if (preg_match_all($regexp, $sql, $matches, PREG_SET_ORDER)) {
@@ -235,6 +246,36 @@ class Schema extends \yii\db\Schema
 	}
 
 	/**
+	 * Returns all unique indexes for the given table.
+	 * Each array element is of the following structure:
+	 *
+	 * ~~~
+	 * [
+	 *	 'IndexName1' => ['col1' [, ...]],
+	 *	 'IndexName2' => ['col2' [, ...]],
+	 * ]
+	 * ~~~
+	 *
+	 * @param TableSchema $table the table metadata
+	 * @return array all unique indexes for the given table.
+	 */
+	public function findUniqueIndexes($table)
+	{
+		$sql = $this->getCreateTableSql($table);
+		$uniqueIndexes = [];
+
+		$regexp = '/UNIQUE KEY\s+([^\(^\s]+)\s*\(([^\)]+)\)/mi';
+		if (preg_match_all($regexp, $sql, $matches, PREG_SET_ORDER)) {
+			foreach ($matches as $match) {
+				$indexName = str_replace('`', '', $match[2]);
+				$indexColumns = array_map('trim', explode(',', str_replace('`', '', $match[3])));
+				$uniqueIndexes[$indexName] = $indexColumns;
+			}
+		}
+		return $uniqueIndexes;
+	}
+
+	/**
 	 * Returns all table names in the database.
 	 * @param string $schema the schema of the tables. Defaults to empty string, meaning the current or default schema.
 	 * @return array all table names in the database. The names have NO schema name prefix.
diff --git a/framework/yii/db/pgsql/Schema.php b/framework/yii/db/pgsql/Schema.php
index eb7de37..96889ab 100644
--- a/framework/yii/db/pgsql/Schema.php
+++ b/framework/yii/db/pgsql/Schema.php
@@ -227,6 +227,74 @@ SQL;
 	}
 
 	/**
+	 * Gets information about given table unique indexes.
+	 * @param TableSchema $table the table metadata
+	 * @return array with index names, columns and if it is an expression tree
+	 */
+	protected function getUniqueIndexInformation($table)
+	{
+		$tableName = $this->quoteValue($table->name);
+		$tableSchema = $this->quoteValue($table->schemaName);
+
+		$sql = <<<SQL
+SELECT
+	i.relname as indexname,
+	ARRAY(
+		SELECT pg_get_indexdef(idx.indexrelid, k + 1, True)
+		FROM generate_subscripts(idx.indkey, 1) AS k
+		ORDER BY k
+	) AS indexcolumns,
+	idx.indexprs IS NOT NULL AS indexprs
+FROM pg_index idx
+INNER JOIN pg_class i ON i.oid = idx.indexrelid
+INNER JOIN pg_class c ON c.oid = idx.indrelid
+INNER JOIN pg_namespace ns ON c.relnamespace = ns.oid
+WHERE idx.indisprimary != True
+AND idx.indisunique = True
+AND c.relname = {$tableName}
+AND ns.nspname = {$tableSchema}
+;
+SQL;
+
+		return $this->db->createCommand($sql)->queryAll();
+	}
+
+	/**
+	 * Returns all unique indexes for the given table.
+	 * Each array element is of the following structure:
+	 *
+	 * ~~~
+	 * [
+	 *	 'IndexName1' => ['col1' [, ...]],
+	 *	 'IndexName2' => ['col2' [, ...]],
+	 * ]
+	 * ~~~
+	 *
+	 * @param TableSchema $table the table metadata
+	 * @return array all unique indexes for the given table.
+	 */
+	public function findUniqueIndexes($table)
+	{
+		$indexes = $this->getUniqueIndexInformation($table);
+		$uniqueIndexes = [];
+
+		foreach ($indexes as $index) {
+			$indexName = $index['indexname'];
+
+			if ($index['indexprs']) {
+				// Index is an expression like "lower(colname::text)"
+				$indexColumns = preg_replace("/.*\(([^\:]+).*/mi", "$1", $index['indexcolumns']);
+			} else {
+				$indexColumns = array_map('trim', explode(',', str_replace(['{', '}'], '', $index['indexcolumns'])));
+			}
+
+			$uniqueIndexes[$indexName] = $indexColumns;
+
+		}
+		return $uniqueIndexes;
+	}
+
+	/**
 	 * Collects the metadata of table columns.
 	 * @param TableSchema $table the table metadata
 	 * @return boolean whether the table exists in the database
diff --git a/framework/yii/db/sqlite/Schema.php b/framework/yii/db/sqlite/Schema.php
index 8633650..9f410b4 100644
--- a/framework/yii/db/sqlite/Schema.php
+++ b/framework/yii/db/sqlite/Schema.php
@@ -159,6 +159,40 @@ class Schema extends \yii\db\Schema
 	}
 
 	/**
+	 * Returns all unique indexes for the given table.
+	 * Each array element is of the following structure:
+	 *
+	 * ~~~
+	 * [
+	 *	 'IndexName1' => ['col1' [, ...]],
+	 *	 'IndexName2' => ['col2' [, ...]],
+	 * ]
+	 * ~~~
+	 *
+	 * @param TableSchema $table the table metadata
+	 * @return array all unique indexes for the given table.
+	 */
+	public function findUniqueIndexes($table)
+	{
+		$sql = "PRAGMA index_list(" . $this->quoteSimpleTableName($table->name) . ')';
+		$indexes = $this->db->createCommand($sql)->queryAll();
+		$uniqueIndexes = [];
+
+		foreach ($indexes as $index) {
+			$indexName = $index['name'];
+			$indexInfo = $this->db->createCommand("PRAGMA index_info(" . $this->quoteValue($index['name']) . ")")->queryAll();
+
+			if ($index['unique']) {
+				$uniqueIndexes[$indexName] = [];
+				foreach ($indexInfo as $row) {
+					$uniqueIndexes[$indexName][] = $row['name'];
+				}
+			}
+		}
+		return $uniqueIndexes;
+	}
+
+	/**
 	 * Loads the column information into a [[ColumnSchema]] object.
 	 * @param array $info column information
 	 * @return ColumnSchema the column schema object