Many mature technologies on this level have been brought out, such as the relational algebra law, the improved logical query plan, the cost estimation of operation, the selective plan based on cost and order of joint, etc . although many methods have been tried out, no remarkable result or noteworthy technology has come to reality because of complexity of data decomposition and network effects 例如,從物理查詢(xún)計(jì)劃的底層磁盤(pán)輸入輸出到語(yǔ)法分析階段的語(yǔ)法分析樹(shù)、用于改進(jìn)查詢(xún)計(jì)劃的代數(shù)定律、邏輯查詢(xún)計(jì)劃的改進(jìn),以及操作代價(jià)的估計(jì)、基于代價(jià)的計(jì)劃和連接順序的選擇等全過(guò)程,都進(jìn)行了不懈的努力。在這方面的研究已經(jīng)非常成熟。