1. 2003 May 24Clive Page Simple ADQL Enhancements Clive Page, AstroGrid Project University of Leicester, UK

2. 2003 May 24Clive Page SELECT INTO newtable SQL designed to specify the final result – which is by default sent to standard output as a table in text form. Astronomers typically want to achieve a result incrementally, checking output of each step. –Need to be able to send results to a temporary table AstroGrid is working on MySpace – users storage area within DBMS or on external file. JHU is working on MyDB – similar concept in DBMS. Exact syntax for may have to be left as implementation-dependent until more experience is gained.

3. 2003 May 24Clive Page EXPLAIN query Most DBMS support the EXPLAIN command, although not part of standard SQL. Very useful to inform user whether a given query will be –Evaluated by sequential scan – very slow for large table –Or use an index – fast even for a large table Results of EXPLAIN are entirely system-dependent –Perhaps this is acceptable at present, we may find a way to present results in a more uniform way later.

4. 2003 May 24Clive Page TOP nrows Already specified in ADQL. Supported by most DBMS: DB2SELECT … WHERE … FETCH FIRST n ROWS ONLY SQL ServerSELECT TOP n … MySQLSELECT … WHERE… LIMIT n OracleSELECT … WHERE… ROWNUM <= n PostgreSQLSELECT … WHERE… LIMIT n Sybase-ASESET ROWCOUNT n; SELECT …

5. 2003 May 24Clive Page TOP nrows - Semantics Syntax well defined, but semantics less so. When used with ORDER BY allows you to get the largest/smallest rows. But: with Sybase-ASE – the use of SET ROWCOUNT with ORDER BY results in selecting the first rows in the table and then sorting them – not usually what is required.

6. 2003 May 24Clive Page Great Circle Distance Function When performing a cross-match it is very often desirable to have the distance between the matching sources as a column in the output Trigonometry to do this is a little complicated –Simplest expression has very poor accuracy with small angles, better to use haversine formula. Propose an additional function to simplify queries: –GCDIST(ra1, dec1, ra2, dec2) –Returns distance in units to be agreed, e.g. degrees, with arguments also in degrees.