Fix where clause in information schema with correct database name

[harshit-gangal]

Overview of the Issue

The query sent down from VTGate to Vttablet does not replace the where clause of the information schema queries for table_schema = 'keyspace' to table_schema = 'databasename'

Reproduction Steps

Steps to reproduce this issue, example:

1. Deploy the following vschema:

   {
     "sharded": false,
     "tables": {
     }
   }

2. Run

mysql> SELECT * FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_SCHEMA = 'commerce' AND TABLE_NAME LIKE '%' HAVING TABLE_TYPE IN ('TABLE','VIEW',null,null,null) ORDER BY TABLE_TYPE, TABLE_SCHEMA, TABLE_NAME;
Empty set (0.02 sec)

mysql> SELECT * FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_SCHEMA = 'commerce' AND COLUMN_NAME LIKE '%' ORDER BY TABLE_SCHEMA, TABLE_NAME, ORDINAL_POSITION;
Empty set (0.00 sec)

Both the query returns empty result test

Binary version

master

Operating system and Environment details

Sprint boot application with mysql 8.0

[harshit-gangal]

Support added via #6638

[yborovikov]

@harshit-gangal this is a (very) breaking change.

[harshit-gangal]

@yborovikov can you explain why this is breaking change? Previously the query did not give any result. Now it is handled.

[yborovikov]

sure: previously a query like SELECT * FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_SCHEMA = 'vt_commerce'; returned a result. now it doesn't.

[harshit-gangal]

Yes, this has changes in vtgate and vttablet. We will make this feature available in two step because now it depends on upgrade order of Vitess cluster.

[yborovikov]

not sure how any sequencing of vitess upgrades can not break the customers that use queries like ... FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_SCHEMA = 'vt_SOMENAMESPACE';.

current client code has to prefix the namespace with vt_ - and the change rendered these queries broken. neither we can not prefix the namespace - since it won't work with current installations of vitess.

the change itself is reasonable - customers shouldn't be aware of internal (to vitess and mysql) re/naming conventions.