Changing duckdb metadata reader

Author: kenshaw

drivers/duckdb/duckdb.go

@@ -5,15 +5,137 @@ package duckdb
 
 import (
 	"context"
+	"database/sql"
+	"fmt"
 	"io"
+	"strings"
 
 	_ "github.com/marcboeker/go-duckdb" // DRIVER
 	"github.com/xo/usql/drivers"
 	"github.com/xo/usql/drivers/metadata"
+	infos "github.com/xo/usql/drivers/metadata/informationschema"
 	mymeta "github.com/xo/usql/drivers/metadata/mysql"
 )
 
+type metaReader struct {
+	metadata.LoggingReader
+}
+
+var (
+	_ metadata.CatalogReader    = &metaReader{}
+	_ metadata.ColumnStatReader = &metaReader{}
+)
+
+func (r metaReader) Catalogs(metadata.Filter) (*metadata.CatalogSet, error) {
+	qstr := `SHOW catalogs`
+	rows, closeRows, err := r.Query(qstr)
+	if err != nil {
+		return nil, err
+	}
+	defer closeRows()
+
+	results := []metadata.Catalog{}
+	for rows.Next() {
+		rec := metadata.Catalog{}
+		err = rows.Scan(&rec.Catalog)
+		if err != nil {
+			return nil, err
+		}
+		results = append(results, rec)
+	}
+	if rows.Err() != nil {
+		return nil, rows.Err()
+	}
+	return metadata.NewCatalogSet(results), nil
+}
+
+func (r metaReader) ColumnStats(f metadata.Filter) (*metadata.ColumnStatSet, error) {
+	names := []string{}
+	if f.Catalog != "" {
+		names = append(names, f.Catalog+".")
+	}
+	if f.Schema != "" {
+		names = append(names, f.Schema+".")
+	}
+	names = append(names, f.Parent)
+	rows, closeRows, err := r.Query(fmt.Sprintf("SHOW STATS FOR %s", strings.Join(names, "")))
+	if err != nil {
+		return nil, err
+	}
+	defer closeRows()
+
+	results := []metadata.ColumnStat{}
+	for rows.Next() {
+		rec := metadata.ColumnStat{Catalog: f.Catalog, Schema: f.Schema, Table: f.Parent}
+		name := sql.NullString{}
+		avgWidth := sql.NullInt32{}
+		numDistinct := sql.NullInt64{}
+		nullFrac := sql.NullFloat64{}
+		numRows := sql.NullInt64{}
+		min := sql.NullString{}
+		max := sql.NullString{}
+		err = rows.Scan(
+			&name,
+			&avgWidth,
+			&numDistinct,
+			&nullFrac,
+			&numRows,
+			&min,
+			&max,
+		)
+		if err != nil {
+			return nil, err
+		}
+		if !name.Valid {
+			continue
+		}
+		rec.Name = name.String
+		if avgWidth.Valid {
+			rec.AvgWidth = int(avgWidth.Int32)
+		}
+		if numDistinct.Valid {
+			rec.NumDistinct = numDistinct.Int64
+		}
+		if nullFrac.Valid {
+			rec.NullFrac = nullFrac.Float64
+		}
+		if min.Valid {
+			rec.Min = min.String
+		}
+		if max.Valid {
+			rec.Max = max.String
+		}
+		results = append(results, rec)
+	}
+	if rows.Err() != nil {
+		return nil, rows.Err()
+	}
+
+	return metadata.NewColumnStatSet(results), nil
+}
+
 func init() {
+	newReader := func(db drivers.DB, opts ...metadata.ReaderOption) metadata.Reader {
+		ir := infos.New(
+			infos.WithPlaceholder(func(int) string { return "?" }),
+			infos.WithCustomClauses(map[infos.ClauseName]string{
+				infos.ColumnsColumnSize:       "0",
+				infos.ColumnsNumericScale:     "0",
+				infos.ColumnsNumericPrecRadix: "0",
+				infos.ColumnsCharOctetLength:  "0",
+			}),
+			infos.WithFunctions(false),
+			infos.WithSequences(false),
+			infos.WithIndexes(false),
+			infos.WithConstraints(false),
+			infos.WithColumnPrivileges(false),
+			infos.WithUsagePrivileges(false),
+		)(db, opts...)
+		mr := &metaReader{
+			LoggingReader: metadata.NewLoggingReader(db, opts...),
+		}
+		return metadata.NewPluginReader(ir, mr)
+	}
 	drivers.Register("duckdb", drivers.Driver{
 		AllowMultilineComments: true,
 		Version: func(ctx context.Context, db drivers.DB) (string, error) {
@@ -24,9 +146,9 @@ func init() {
 			}
 			return "DuckDB " + ver, nil
 		},
-		NewMetadataReader: mymeta.NewReader,
+		NewMetadataReader: newReader,
 		NewMetadataWriter: func(db drivers.DB, w io.Writer, opts ...metadata.ReaderOption) metadata.Writer {
-			return metadata.NewDefaultWriter(mymeta.NewReader(db, opts...))(db, w)
+			return metadata.NewDefaultWriter(newReader(db, opts...))(db, w)
 		},
 		Copy:         drivers.CopyWithInsert(func(int) string { return "?" }),
 		NewCompleter: mymeta.NewCompleter,