在MySQL數據庫的列中計數值的查詢

Question

我有一個MySQL查詢，按月將我的數據庫中的所有ClientCostToDate行（類型爲DECIMAL）相加，然後將數據作爲JSON返回。

我的PHP腳本是：

//the sql query to be executed 
$estimates_query = "SELECT DATE_FORMAT(CreatedDate, '%M %Y') AS CreatedMonth, 
SUM(ClientCostToDate) AS ClientCostsTotal, 
EXTRACT(YEAR_MONTH FROM CreatedDate) AS CreatedYearMonth 
FROM Estimates 
WHERE CreatedDate IS NOT NULL 
AND EXTRACT(YEAR_MONTH FROM CreatedDate) >= EXTRACT(YEAR_MONTH FROM CURDATE())-100 
GROUP BY DATE_FORMAT(CreatedDate, '%M') 
ORDER BY CreatedYearMonth"; 

//storing the result of the executed query 
$result = $conn->query($estimates_query); 

//initialize the array to store the processed data 
$estimatesJsonArray = array(); 

//check if there is any data returned by the sql query 
if ($result->num_rows > 0) { 
//converting the results into an associative array 
while ($row = $result->fetch_assoc()) { 
$jsonArrayItem = array(); 
$jsonArrayItem['date'] = $row['CreatedMonth']; 
$jsonArrayItem['clientCostsTotal'] = $row['ClientCostsTotal']; 
//append the above created object into the main array 
array_push($estimatesJsonArray, $jsonArrayItem); 
} 
} 

//close the connection to the database 
$conn->close(); 

//set the response content type as json 
header('Content-type: application/json'); 
//output the return value of json encode using the echo function 
echo json_encode($estimatesJsonArray, JSON_PRETTY_PRINT); 

這裏是JSON：

[ 
{ 
    "date": "February 2016", 
    "clientCostsTotal": "21211.25" 
}, 
{ 
    "date": "March 2016", 
    "clientCostsTotal": "206996.25" 
}, 
{ 
    "date": "April 2016", 
    "clientCostsTotal": "74667.50" 
}, 
{ 
    "date": "May 2016", 
    "clientCostsTotal": "61128.75" 
}, 
{ 
    "date": "June 2016", 
    "clientCostsTotal": "267740.50" 
}, 
{ 
    "date": "July 2016", 
    "clientCostsTotal": "200946.75" 
}, 
{ 
    "date": "August 2016", 
    "clientCostsTotal": "0.00" 
} 
] 

有一個在MySQL數據庫Status（VARCHAR型）的另一列。它包含以下值：新估計，已批准，已開票，正在等待結算，已取消，有客戶，已提交成本。

我需要編寫一個MySQL查詢，該查詢給出了組成SUM(ClientCostToDate) AS ClientCostsTotal的行的所有狀態。然後，我需要計算每種狀態的數量（新估計，已批准，已開票，等待結算，已取消，有客戶，已提交成本）。什麼是完成這個最好的方法？

Answer 1

你可以把每個值在一個單獨的列，使用條件彙總：

SELECT DATE_FORMAT(CreatedDate, '%M %Y') AS CreatedMonth, 
     SUM(ClientCostToDate) AS ClientCostsTotal, 
     SUM(status = 'New Estimate') as num_NewEstimate, 
     SUM(status = 'Approved') as num_Approved, 
     . . . 
FROM Estimates 
WHERE CreatedDate IS NOT NULL AND 
     EXTRACT(YEAR_MONTH FROM CreatedDate) >= EXTRACT(YEAR_MONTH FROM CURDATE())-100 
GROUP BY DATE_FORMAT(CreatedDate, '%M %Y') 
ORDER BY CreatedYearMonth;