// expandWildcards returns a new SelectStatement with wildcards expanded
// If only a `SELECT *` is present, without a `GROUP BY *`, both tags and fields expand in the SELECT
// If a `SELECT *` and a `GROUP BY *` are both present, then only fiels are expanded in the `SELECT` and only
// tags are expanded in the `GROUP BY`
func (lm *SelectMapper) expandWildcards(stmt *influxql.SelectStatement) (*influxql.SelectStatement, error) {
// If there are no wildcards in the statement, return it as-is.
if !stmt.HasWildcard() {
return stmt, nil
}
// Use sets to avoid duplicate field names.
fieldSet := map[string]struct{}{}
dimensionSet := map[string]struct{}{}
var fields influxql.Fields
var dimensions influxql.Dimensions
// keep track of where the wildcards are in the select statement
hasFieldWildcard := stmt.HasFieldWildcard()
hasDimensionWildcard := stmt.HasDimensionWildcard()
// Iterate measurements in the FROM clause getting the fields & dimensions for each.
for _, src := range stmt.Sources {
if m, ok := src.(*influxql.Measurement); ok {
// Lookup the measurement in the database.
mm := lm.shard.index.Measurement(m.Name)
if mm == nil {
// This shard have never received data for the measurement. No Mapper
// required.
return stmt, nil
}
// Get the fields for this measurement.
for _, name := range mm.FieldNames() {
if _, ok := fieldSet[name]; ok {
continue
}
fieldSet[name] = struct{}{}
fields = append(fields, &influxql.Field{Expr: &influxql.VarRef{Val: name}})
}
// Add tags to fields if a field wildcard was provided and a dimension wildcard was not.
if hasFieldWildcard && !hasDimensionWildcard {
for _, t := range mm.TagKeys() {
if _, ok := fieldSet[t]; ok {
continue
}
fieldSet[t] = struct{}{}
fields = append(fields, &influxql.Field{Expr: &influxql.VarRef{Val: t}})
}
}
// Get the dimensions for this measurement.
if hasDimensionWildcard {
for _, t := range mm.TagKeys() {
if _, ok := dimensionSet[t]; ok {
continue
}
dimensionSet[t] = struct{}{}
dimensions = append(dimensions, &influxql.Dimension{Expr: &influxql.VarRef{Val: t}})
}
}
}
}
// Return a new SelectStatement with the wild cards rewritten.
return stmt.RewriteWildcards(fields, dimensions), nil
}
