feat(client): add a postgres database querier that implements databas…

…e querier interface

pkg/client/postgres.go

@@ -0,0 +1,93 @@
+package client
+
+import (
+	"fmt"
+
+	sq "github.com/Masterminds/squirrel"
+	_ "github.com/go-sql-driver/mysql"
+	_ "github.com/lib/pq"
+	_ "modernc.org/sqlite"
+)
+
+type postgres struct {
+}
+
+func (p *postgres) ShowTables(schema string) (string, []interface{}, error) {
+	var (
+		query string
+		err   error
+		args  []interface{}
+	)
+	psql := sq.StatementBuilder.PlaceholderFormat(sq.Dollar)
+	query, args, err = psql.Select("table_name").
+		From("information_schema.tables").
+		Where(sq.Eq{"table_schema": schema}).
+		OrderBy("table_name").
+		ToSql()
+	if err != nil {
+		return "", nil, err
+	}
+
+	return query, args, nil
+}
+func (p *postgres) TableStructure(tableName, schema string) (string, []interface{}, error) {
+	psql := sq.StatementBuilder.PlaceholderFormat(sq.Dollar)
+
+	query, args, err := psql.Select(
+		"c.column_name",
+		"c.is_nullable",
+		"c.data_type",
+		"c.character_maximum_length",
+		"c.numeric_precision",
+		"c.numeric_scale",
+		"c.ordinal_position",
+		"tc.constraint_type AS pkey",
+	).
+		From("information_schema.columns AS c").
+		LeftJoin(
+			`information_schema.constraint_column_usage AS ccu
+					ON c.table_schema = ccu.table_schema
+						AND c.table_name = ccu.table_name
+						AND c.column_name = ccu.column_name`,
+		).
+		LeftJoin(
+			`information_schema.table_constraints AS tc
+					ON ccu.constraint_schema = tc.constraint_schema
+						AND ccu.constraint_name = tc.constraint_name`,
+		).
+		Where(
+			sq.And{
+				sq.Eq{"c.table_schema": schema},
+				sq.Eq{"c.table_name": tableName},
+			},
+		).
+		ToSql()
+	return query, args, err
+}
+
+func (p *postgres) Constraints(tableName, schema string) (string, []interface{}, error) {
+	var (
+		query sq.SelectBuilder
+		sql   string
+	)
+
+	query = sq.Select(
+		`tc.constraint_name`,
+		`tc.table_name`,
+		`tc.constraint_type`,
+	).
+		From("information_schema.table_constraints AS tc").
+		Where("tc.table_name = ?")
+	query = query.Where(fmt.Sprintf("tc.table_schema = '%s'", schema))
+	query = query.PlaceholderFormat(sq.Dollar)
+
+	sql, _, err := query.ToSql()
+	if err != nil {
+		return "", nil, err
+	}
+	return sql, nil, err
+}
+
+func (p *postgres) Indexes(tableName string) string {
+	return "SELECT * FROM pg_indexes WHERE tablename = $1;"
+}