user: Question: What is the sum of Year with a Type of Informal, and a Location with Justus Lipsius building, Brussels, and a Date with 23 May?
Columns: ['Year', 'Date', 'Type', 'President', 'Location']
Types: ['real', 'text', 'text', 'text', 'text']
Sample row: [2010.0, '11 February', 'Informal', 'Herman Van Rompuy (1st term)', 'Solvay Library , Brussels']
SQL:

assistant: SELECT SUM("Year") FROM "Table" WHERE "Type" = 'Informal' AND "Location" = 'Justus Lipsius building, Brussels' AND "Date" = '23 May';