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記憶體
0xFFFF
0x0000
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123456
Int
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可以放0或1
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如果是1,則表示數值是負數
如果是0,則表示數值是正數
31個位元用來表示數值
連結
符號位元
指數位元 小數(尾數)部分
以雙精準度(Double)型別為例子:
•
•
•
•
•
•
•
•
•
•
•
• 流水號不需要負數,如果宣告成INT,我們會有2147483647種數
值是完全用不到的。但如果宣告成UNSIGNED INT 我們便能增加正
數所能表示的範圍,充分利用變數空間。
•
• 如果一筆資料它的數值範圍只有0~200,通常人的體重也只在這個範圍
內,那我們不需要用整數來存放這個資料,可以選擇用BYTE或CHAR來存
放這個資料,尤其在資料庫系統中,資料數量龐大就能明顯發現資料型
別的不同所造成執行效率上的差異。
•
• 若將日期以字串的形式儲存,要分別取出年、月、日得再做字串處理
• 若將日期以DATE或相應的日期資料型別儲存,通常有對應的方法可以直接取出
年、月、日,如YEAR=DATE.YEAR()
關於資料型態
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