seaweedfs/weed/query/engine/describe.go

package engine

import (
	"context"
	"fmt"
	"strings"
	
	"github.com/seaweedfs/seaweedfs/weed/query/sqltypes"
	"github.com/xwb1989/sqlparser"
)

// executeDescribeStatement handles DESCRIBE table commands
// Assumption: DESCRIBE shows table schema in MySQL-compatible format
func (e *SQLEngine) executeDescribeStatement(ctx context.Context, tableName string, database string) (*QueryResult, error) {
	if database == "" {
		database = e.catalog.GetCurrentDatabase()
		if database == "" {
			database = "default"
		}
	}
	
	// Get topic schema from broker
	recordType, err := e.catalog.brokerClient.GetTopicSchema(ctx, database, tableName)
	if err != nil {
		return &QueryResult{Error: err}, err
	}
	
	// Format schema as DESCRIBE output
	result := &QueryResult{
		Columns: []string{"Field", "Type", "Null", "Key", "Default", "Extra"},
		Rows:    make([][]sqltypes.Value, len(recordType.Fields)),
	}
	
	for i, field := range recordType.Fields {
		sqlType := e.convertMQTypeToSQL(field.Type)
		
		result.Rows[i] = []sqltypes.Value{
			sqltypes.NewVarChar(field.Name),           // Field
			sqltypes.NewVarChar(sqlType),              // Type
			sqltypes.NewVarChar("YES"),                // Null (assume nullable)
			sqltypes.NewVarChar(""),                   // Key (no keys for now)
			sqltypes.NewVarChar("NULL"),               // Default
			sqltypes.NewVarChar(""),                   // Extra
		}
	}
	
	return result, nil
}

// Enhanced executeShowStatementWithDescribe handles SHOW statements including DESCRIBE
func (e *SQLEngine) executeShowStatementWithDescribe(ctx context.Context, stmt *sqlparser.Show) (*QueryResult, error) {
	switch strings.ToUpper(stmt.Type) {
	case "DATABASES":
		return e.showDatabases(ctx)
	case "TABLES":
		// TODO: Parse FROM clause properly for database specification
		return e.showTables(ctx, "")
	case "COLUMNS":
		// SHOW COLUMNS FROM table is equivalent to DESCRIBE
		if stmt.OnTable.Name.String() != "" {
			tableName := stmt.OnTable.Name.String()
			database := ""
			if stmt.OnTable.Qualifier.String() != "" {
				database = stmt.OnTable.Qualifier.String()
			}
			return e.executeDescribeStatement(ctx, tableName, database)
		}
		fallthrough
	default:
		err := fmt.Errorf("unsupported SHOW statement: %s", stmt.Type)
		return &QueryResult{Error: err}, err
	}
}

// Add support for DESCRIBE as a separate statement type
// This would be called from ExecuteSQL if we detect a DESCRIBE statement
func (e *SQLEngine) handleDescribeCommand(ctx context.Context, sql string) (*QueryResult, error) {
	// Simple parsing for "DESCRIBE table_name" format
	// TODO: Use proper SQL parser for more robust parsing
	parts := strings.Fields(strings.TrimSpace(sql))
	if len(parts) < 2 {
		err := fmt.Errorf("DESCRIBE requires a table name")
		return &QueryResult{Error: err}, err
	}
	
	tableName := parts[1]
	database := ""
	
	// Handle database.table format
	if strings.Contains(tableName, ".") {
		parts := strings.SplitN(tableName, ".", 2)
		database = parts[0]
		tableName = parts[1]
	}
	
	return e.executeDescribeStatement(ctx, tableName, database)
}