如何在 javascript 或 MySQL 中对数据透视动态数组进行分组？

Question

基本上我想旋转动态数组，例如我从 MySQL 表中得到的这个数组：

[ { ruleAlias: 'DEMAND', date: '2019-03-22', count: 10 },
  { ruleAlias: 'VOUCHER', date: '2019-03-25', count: 20 },
  { ruleAlias: 'DEMAND', date: '2019-03-25', count: 10 },
  { ruleAlias: 'BILL', date: '2019-03-25', count: 2 },
  { ruleAlias: 'BILL', date: '2019-05-06', count: 1 } ]

我希望这个数组变成：

[ ['RULE', 'DEMAND', 'VOUCHER', 'BILL'],
  ['2019-03-22', 10, 0, 0],
  ['2019-03-25', 10, 20, 2],
  ['2019-05-06', 0, 0, 1]
]

这是我使用的 MySQL 查询：

SELECT ruleAlias, date, count
FROM (
    SELECT ruleAlias, DATE_FORMAT(createDate, '%Y-%m-%d') AS date, COUNT(DATE_FORMAT(createDate, '%Y-%m-%d')) AS count FROM histPoint WHERE ruleAlias IN (SELECT alias FROM mstRule WHERE clientId = 5) AND YEAR(createDate) = YEAR(CURDATE()) GROUP BY date, ruleAlias
) AS t

我得到的数据是动态的，例如上面的数据是3条规则，但是表中的数据可以得到3条以上的规则，如何在javascript中将这种数组pivot到预期的输出或直接在sql中pivot？

Answer 1

您可以使用哈希表并收集给定日期/规则对的所有值。然后构建一个表，并为未给定的对使用默认零。

const key = (...a) => a.join('|');

var data = [{ ruleAlias: 'DEMAND', date: '2019-03-22', count: 10 }, { ruleAlias: 'VOUCHER', date: '2019-03-25', count: 20 }, { ruleAlias: 'DEMAND', date: '2019-03-25', count: 10 }, { ruleAlias: 'BILL', date: '2019-03-25', count: 2 }, { ruleAlias: 'BILL', date: '2019-05-06', count: 1 }],
    temp = {},
    result,
    dates = new Set,
    rules = new Set;

data.forEach(({ ruleAlias, date, count }) => {
    dates.add(date);
    rules.add(ruleAlias);
    temp[key(date, ruleAlias)] = (temp[key(date, ruleAlias)] || 0) + count;
});    

result = [
    ['RULE', ...rules],
    ...Array.from(dates, date => [
        date,
         ...Array.from(rules, rule => temp[key(date, rule)] || 0)
    ])
];

console.log(result);

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