MySQL 5.5

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Records: 4  Duplicates: 0  Warnings: 0

Records: 3  Duplicates: 0  Warnings: 0

id	date	amount1
1	2021-02-24	100
2	2021-02-25	200
3	2021-02-26	300
4	2021-02-26	400

id	date	amount2
1	2021-02-24	500
2	2021-02-25	600
3	2021-02-25	700

SELECT dates.`date`, 
       COALESCE(data21.amount1, 0) amount1, 
       COALESCE(data22.amount2, 0) amount2
FROM ( SELECT `date`, row_number11 row_number
       FROM ( SELECT table1.*, 
                     @row_number11 := CASE WHEN @date11 = table1.`date`
                                           THEN @row_number11 + 1
                                           ELSE 1 END row_number11,
                     @date11 := table1.`date` date1
              FROM table1
              CROSS JOIN ( SELECT @date11:=NULL, @row_number11:= 0 ) variables
              ORDER BY table1.`date`, table1.id
            ) data11
       UNION 
       SELECT `date`, row_number12 row_number
       FROM ( SELECT table2.*, 
                     @row_number12 := CASE WHEN @date12 = table2.`date`
                                           THEN @row_number12 + 1
                                           ELSE 1 END row_number12,
                     @date12 := table2.`date` date2
              FROM table2
              CROSS JOIN ( SELECT @date12:=NULL, @row_number12:= 0 ) variables
              ORDER BY table2.`date`, table2.id
            ) data12
       ) dates
LEFT JOIN ( SELECT table1.*, 
                   @row_number21 := CASE WHEN @date21 = table1.`date`
                                    THEN @row_number21 + 1
                                    ELSE 1 END row_number21,
                   @date21 := table1.`date` date1
            FROM table1
            CROSS JOIN ( SELECT @date21:=NULL, @row_number21:= 0 ) variables
            ORDER BY table1.`date`, table1.id
          ) data21 ON dates.`date` = data21.`date` 
                  AND dates.row_number = data21.row_number21
LEFT JOIN ( SELECT table2.*, 
                   @row_number22 := CASE WHEN @date22 = table2.`date`
                                    THEN @row_number22 + 1
                                    ELSE 1 END row_number22,
                   @date22 := table2.`date` date2
            FROM table2
            CROSS JOIN ( SELECT @date22:=NULL, @row_number22:= 0 ) variables
            ORDER BY table2.`date`, table2.id
          ) data22 ON dates.`date` = data22.`date` 
                  AND dates.row_number = data22.row_number22
ORDER BY `date`

date	amount1	amount2
2021-02-24	100	500
2021-02-25	200	600
2021-02-25	0	700
2021-02-26	300	0
2021-02-26	400	0