Mono repo -> Master (#22553)

Combines the following repositories into one:

https://github.com/mattermost/mattermost-server
https://github.com/mattermost/mattermost-webapp
https://github.com/mattermost/focalboard
https://github.com/mattermost/mattermost-plugin-playbooks

server/channels/db/migrations/mysql/000049_create_channels.down.sql

@@ -0,0 +1,136 @@
+SET @preparedStatement = (SELECT IF(
+    (
+        SELECT COUNT(*) FROM INFORMATION_SCHEMA.STATISTICS
+        WHERE table_name = 'Channels'
+        AND table_schema = DATABASE()
+        AND index_name = 'idx_channels_name'
+    ) > 0,
+    'SELECT 1',
+    'CREATE INDEX idx_channels_name ON Channels(Name);'
+));
+
+PREPARE createIndexIfNotExists FROM @preparedStatement;
+EXECUTE createIndexIfNotExists;
+DEALLOCATE PREPARE createIndexIfNotExists;
+
+SET @preparedStatement = (SELECT IF(
+    (
+        SELECT COUNT(*) FROM INFORMATION_SCHEMA.COLUMNS
+        WHERE table_name = 'Channels'
+        AND table_schema = DATABASE()
+        AND column_name = 'Shared'
+    ) > 0,
+    'ALTER TABLE Channels DROP COLUMN Shared;',
+    'SELECT 1'
+));
+
+PREPARE alterIfExists FROM @preparedStatement;
+EXECUTE alterIfExists;
+DEALLOCATE PREPARE alterIfExists;
+
+SET @preparedStatement = (SELECT IF(
+    (
+        SELECT COUNT(*) FROM INFORMATION_SCHEMA.STATISTICS
+        WHERE table_name = 'Channels'
+        AND table_schema = DATABASE()
+        AND index_name = 'idx_channels_scheme_id'
+    ) > 0,
+    'DROP INDEX idx_channels_scheme_id ON Channels;',
+    'SELECT 1'
+));
+
+PREPARE removeIndexIfExists FROM @preparedStatement;
+EXECUTE removeIndexIfExists;
+DEALLOCATE PREPARE removeIndexIfExists;
+
+SET @preparedStatement = (SELECT IF(
+    (
+        SELECT column_type FROM INFORMATION_SCHEMA.COLUMNS
+        WHERE table_name = 'Channels'
+        AND table_schema = DATABASE()
+        AND column_name = 'GroupConstrained'
+    ) != 'tinyint(4)',
+    'ALTER TABLE Channels MODIFY GroupConstrained tinyint(4);',
+    'SELECT 1'
+));
+
+PREPARE alterIfTypeDifferent FROM @preparedStatement;
+EXECUTE alterIfTypeDifferent;
+DEALLOCATE PREPARE alterIfTypeDifferent;
+
+SET @preparedStatement = (SELECT IF(
+    (
+        SELECT COUNT(*) FROM INFORMATION_SCHEMA.COLUMNS
+        WHERE table_name = 'Channels'
+        AND table_schema = DATABASE()
+        AND column_name = 'GroupConstrained'
+    ) > 0,
+    'ALTER TABLE Channels DROP COLUMN GroupConstrained;',
+    'SELECT 1'
+));
+
+PREPARE alterIfExists FROM @preparedStatement;
+EXECUTE alterIfExists;
+DEALLOCATE PREPARE alterIfExists;
+
+SET @preparedStatement = (SELECT IF(
+    (
+        SELECT COUNT(*) FROM INFORMATION_SCHEMA.STATISTICS
+        WHERE table_name = 'Channels'
+        AND table_schema = DATABASE()
+        AND index_name = 'idx_channels_txt'
+    ) > 0,
+    'SELECT 1',
+    'CREATE INDEX idx_channels_txt ON Channels(Name,DisplayName);'
+));
+
+PREPARE createIndexIfNotExists FROM @preparedStatement;
+EXECUTE createIndexIfNotExists;
+DEALLOCATE PREPARE createIndexIfNotExists;
+
+SET @preparedStatement = (SELECT IF(
+    (
+        SELECT COUNT(*) FROM INFORMATION_SCHEMA.COLUMNS
+        WHERE table_name = 'Channels'
+        AND table_schema = DATABASE()
+        AND column_name = 'SchemeId'
+    ) > 0,
+    'ALTER TABLE Channels DROP COLUMN SchemeId;',
+    'SELECT 1'
+));
+
+PREPARE alterIfExists FROM @preparedStatement;
+EXECUTE alterIfExists;
+DEALLOCATE PREPARE alterIfExists;
+
+SET @preparedStatement = (SELECT IF(
+    (
+        SELECT COUNT(*) FROM INFORMATION_SCHEMA.STATISTICS
+        WHERE table_name = 'Channels'
+        AND table_schema = DATABASE()
+        AND index_name = 'idx_channels_displayname'
+    ) > 0,
+    'SELECT 1',
+    'CREATE INDEX idx_channels_displayname ON Channels(DisplayName);'
+));
+
+PREPARE createIndexIfNotExists FROM @preparedStatement;
+EXECUTE createIndexIfNotExists;
+DEALLOCATE PREPARE createIndexIfNotExists;
+
+SET @preparedStatement = (SELECT IF(
+    (
+        SELECT column_type FROM INFORMATION_SCHEMA.COLUMNS
+        WHERE table_name = 'Channels'
+        AND table_schema = DATABASE()
+        AND column_name = 'Purpose'
+    ) != 'varchar(64)',
+    'ALTER TABLE Channels MODIFY Purpose varchar(64);',
+    'SELECT 1'
+));
+
+PREPARE alterIfTypeDifferent FROM @preparedStatement;
+EXECUTE alterIfTypeDifferent;
+DEALLOCATE PREPARE alterIfTypeDifferent;
+
+DROP TABLE IF EXISTS Channels;