Class Select

src/main/java/com/sql/parse/statement/impl/druid/Select.java:26–526

@date 2019年4月29日上午11:32:02 @desc Select语法操作类

 * @desc Select语法操作类
 */
public class Select extends com.sql.parse.statement.Select {
    private SQLSelectStatement select;

    public Select(SQLSelectStatement select) {
        this.select = select;
    }

    public Select(Table table) {
        String sql = "select * from " + table.getTableName();
        if (table.getAlias() != null) {
            sql += " " + table.getAlias();
        }
        List<SQLStatement> sqlStatementList = SQLUtils.parseStatements(sql, SqlParseConfig.getDbType());
        SQLSelectStatement select = (SQLSelectStatement) sqlStatementList.get(0);
        this.select = select;
    }

    public Select(String tableName) {
        this(new Table(tableName));
    }

    /*public Select(Owner table, SelectItem... columns) {
        if(columns.length==0){
            this.select = SelectUtils.buildSelectFromTable(table.getTable());
        }else{
            SelectExpressionItem[] array = new SelectExpressionItem[columns.length];
            for (int i = 0; i < columns.length; i++) {
                array[i] = columns[i].getColumn();
            }
            this.select = SelectUtils.buildSelectFromTableAndSelectItems(table.getTable(), array);
        }
    }*/

    @Override
    public String getSql(boolean safe) {
        /*where条件为空时，添加[rownum<500]或[limit 500]的条件表达式*/
        Select mySelect = this.clone();
        SQLSelectQueryBlock queryBlock = select.getSelect().getQueryBlock();
        if (queryBlock.getLimit() == null) {
            boolean flag = true;
            List<SQLSelectItem> selectItems = queryBlock.getSelectList();
            if (selectItems.size() == 1) {
               SQLSelectItem selectItem = selectItems.get(0);
               SQLExpr expression = selectItem.getExpr();
                if (expression instanceof SQLAggregateExpr && "count".equals(((SQLAggregateExpr) expression).getMethodName().toLowerCase())) {
                    flag = false;
                }
            }
            if (queryBlock.getWhere() != null) {
                flag = false;
            }
            if (safe && flag) {
                mySelect.limit(500);
            }
        }
        return SQLUtils.toSQLString(mySelect.getSelect());
    }