[5.5] Better temporary tables support

[paulofreitas]

TL;DR

• Currently we can't use $table->temporary(); option to create temporary tables when using the SQL Server even it supporting them - within this driver it's a no-op command (it's the only one that is missing this)

• This PR adds this missing functionality to SQL Server, therefore making it usable with any database driver

• Since SQL Server can create both local and global temporary tables and all other drivers can create only local temporary tables, we'll be offering this as a shortcut for creating local temporary tables - developers would still be allowed to create SQL Server's temporary tables in the driver-specific way (by prefixing their name)

• This PR also adds missing tests for temporary tables creation

Proposal

Currently we have true temporary tables support for MySQL, PostgreSQL and SQLite. They're using the same CREATE TEMPORARY TABLE syntax based on SQL-92 standard although none of them follow it strictly - they're just vendor implementations. SQL Server temporary tables can be manually created by prefixing them with a single number sign # for local temporary tables and a double number sign ## for global temporary tables - so presently we could be using the existing $table->setTablePrefix() method to create temporary tables in SQL Server.

Though it does support temporary tables, using $table->temporary(); will be a no-op command when using SQL Server. I'm proposing that we start matching the developer expectation by creating temporary tables as requested. Since SQL Server have support for both local and global temporary tables and all other databases have support for local temporary tables only, it seems reasonable to follow their behavior.

Implementation

We'll be just overloading Illuminate\Database\Schema\Grammars\SqlServerGrammar->wrapTable() method to honor the $table->temporary option and call the SqlServerGrammar->setTablePrefix() method to prefix the table with a single number sign. It's being changed here because any method that create/modify/drop the table would need the prefixed table name.

Changes

I'm targeting this to 5.5 because it's an unsupported feature for SQL Server users - Laravel would allow you to use $table->temporary(); no matter what but it will be a no-op command. Implementing this in 5.5 would just match the usage expectation for those who were using it albeit being unsupported. I can however quickly promote it to 5.6 if prompted.

Code

• Illuminate\Database\Schema\Grammars\SqlServerGrammar
  • Added wrapTable() method overloading to prefix the table name.

Tests

4 new tests and 8 new assertions

• Illuminate\Tests\Database\DatabaseMySqlSchemaGrammarTest
• Illuminate\Tests\Database\DatabasePostgresSchemaGrammarTest
• Illuminate\Tests\Database\DatabaseSQLiteSchemaGrammarTest
• Illuminate\Tests\Database\DatabaseSqlServerSchemaGrammarTest
  • Added missing tests for temporary tables creation in a new testCreateTemporaryTable() method.