func (d *dbBasePostgres) DbTypes() map[string]string {
	return postgresTypes
}
get column types of postgresql.
package orm
import (
	"fmt"
	"strconv"
)
var postgresOperators = map[string]string{
	"exact":       "= ?",
	"iexact":      "= UPPER(?)",
	"contains":    "LIKE ?",
	"icontains":   "LIKE UPPER(?)",
	"gt":          "> ?",
	"gte":         ">= ?",
	"lt":          "< ?",
	"lte":         "<= ?",
	"eq":          "= ?",
	"ne":          "!= ?",
	"startswith":  "LIKE ?",
	"endswith":    "LIKE ?",
	"istartswith": "LIKE UPPER(?)",
	"iendswith":   "LIKE UPPER(?)",
}
var postgresTypes = map[string]string{
	"auto":            "serial NOT NULL PRIMARY KEY",
	"pk":              "NOT NULL PRIMARY KEY",
	"bool":            "bool",
	"string":          "varchar(%d)",
	"string-text":     "text",
	"time.Time-date":  "date",
	"time.Time":       "timestamp with time zone",
	"int8":            `smallint CHECK("%COL%" >= -127 AND "%COL%" <= 128)`,
	"int16":           "smallint",
	"int32":           "integer",
	"int64":           "bigint",
	"uint8":           `smallint CHECK("%COL%" >= 0 AND "%COL%" <= 255)`,
	"uint16":          `integer CHECK("%COL%" >= 0)`,
	"uint32":          `bigint CHECK("%COL%" >= 0)`,
	"uint64":          `bigint CHECK("%COL%" >= 0)`,
	"float64":         "double precision",
	"float64-decimal": "numeric(%d, %d)",
	"json":            "json",
	"jsonb":           "jsonb",
}
type dbBasePostgres struct {
	dbBase
}
var _ dbBaser = new(dbBasePostgres)
func (d *dbBasePostgres) OperatorSQL(operator string) string {
	return postgresOperators[operator]
}
func (d *dbBasePostgres) GenerateOperatorLeftCol(fi *fieldInfo, operator string, leftCol *string) {
	switch operator {
	case "contains", "startswith", "endswith":
		*leftCol = fmt.Sprintf("%s::text", *leftCol)
	case "iexact", "icontains", "istartswith", "iendswith":
		*leftCol = fmt.Sprintf("UPPER(%s::text)", *leftCol)
	}
}
func (d *dbBasePostgres) SupportUpdateJoin() bool {
	return false
}
func (d *dbBasePostgres) MaxLimit() uint64 {
	return 0
}
func (d *dbBasePostgres) TableQuote() string {
	return `"`
}
// postgresql value placeholder is $n.
// replace default ? to $n.
func (d *dbBasePostgres) ReplaceMarks(query *string) {
	q := *query
	num := 0
	for _, c := range q {
		if c == '?' {
			num++
		}
	}
	if num == 0 {
		return
	}
	data := make([]byte, 0, len(q)+num)
	num = 1
	for i := 0; i < len(q); i++ {
		c := q[i]
		if c == '?' {
			data = append(data, '$')
			data = append(data, []byte(strconv.Itoa(num))...)
			num++
		} else {
			data = append(data, c)
		}
	}
	*query = string(data)
}
// make returning sql support for postgresql.
func (d *dbBasePostgres) HasReturningID(mi *modelInfo, query *string) bool {
	fi := mi.fields.pk
	if fi.fieldType&IsPositiveIntegerField == 0 && fi.fieldType&IsIntegerField == 0 {
		return false
	}
	if query != nil {
		*query = fmt.Sprintf(`%s RETURNING "%s"`, *query, fi.column)
	}
	return true
}
// sync auto key
func (d *dbBasePostgres) setval(db dbQuerier, mi *modelInfo, autoFields []string) error {
	if len(autoFields) == 0 {
		return nil
	}
	Q := d.ins.TableQuote()
	for _, name := range autoFields {
		query := fmt.Sprintf("SELECT setval(pg_get_serial_sequence('%s', '%s'), (SELECT MAX(%s%s%s) FROM %s%s%s));",
			mi.table, name,
			Q, name, Q,
			Q, mi.table, Q)
		if _, err := db.Exec(query); err != nil {
			return err
		}
	}
	return nil
}
// show table sql for postgresql.
func (d *dbBasePostgres) ShowTablesQuery() string {
	return "SELECT table_name FROM information_schema.tables WHERE table_type = 'BASE TABLE' AND table_schema NOT IN ('pg_catalog', 'information_schema')"
}
// show table columns sql for postgresql.
func (d *dbBasePostgres) ShowColumnsQuery(table string) string {
	return fmt.Sprintf("SELECT column_name, data_type, is_nullable FROM information_schema.columns where table_schema NOT IN ('pg_catalog', 'information_schema') and table_name = '%s'", table)
}