TRUNCATE TABLE not working on DB engines

[seb-ster]

TRUNCATE TABLE works on 'in memory' DB. But using Local Storage DB returns error:

A.engines[r.engineid].truncateTable is not a function

Seems Truncating is done in the line where the yy.TruncateTable.prototype.execute method is defined.

For in 'in memory' DBs the line db.tables[tableid].data = []; is called, thus the Table is empty.

For other DB engines the method alasql.engines[db.engineid].truncateTable(this.table.databaseid || databaseid,tableid, this.ifexists, cb); is called.
It seems this method is not defined for any DB engine.

file: alasql.js
version: 0.3.2
on FF49.0.1, W10

[seb-ster]

A work around is:
DELETE FROM [table name]
but this will not reset AUTOINCREMENT/IDENTITY values on this table

note: AUTOINCREMENT/IDENTITY is not yet working on DB engines as per #462

[seb-ster]

I wrote and tested a truncateTable method for Local Storage:
This also also resets AUTOINCREMENT/IDENTITY values on this table

/**
   Empty table and reset identities
   @param databaseid {string} AlaSQL database id (not external localStorage)
   @param tableid {string} Table name
   @param ? i dont know what the 3rd argument is
   @param cb {function} Callback
   @return 1 on success
*/
LS.truncateTable = function(databaseid,tableid, unknown, cb){
  var res = 1
  var db = alasql.databases[databaseid];
  var tbl = LS.get(db.lsdbid+'.'+tableid);
  //clear data from table
  tbl.data = [];
  //reset all identities to 1
  for (var field in tbl.identities) {
    tbl.identities[field].value = 1;
  }

  db.tables[tableid] = tbl;

  if(cb)
     res = cb(res);

  return res;
}

[mathiasrw]

This is great! lets get it into the code.

Would yo like to make a PR and get credits for the contribution, or would you prefer that I just extend the src with your input here?

[seb-ster]

@mathiasrw
Hi, just did the PR (had not done that before)