90th Percentile Spend per Card Tier

SQL practice question · Hard · Analytics · American Express

First compute each card member's total spend (refunds are negative amounts and reduce the total). Then, per tier, find the 90th percentile of member totals using the nearest-rank method, WITHOUT percentile functions: sort totals ascending and take the value at position CEIL(0.9 * n), where n is the number of members in the tier. Return tier, members (n), p90_spend (ROUND 2) and members_at_or_above (members whose total >= p90_spend). Order by tier.

Table: card_spend

Schema of card_spend
ColumnType
txn_idINTEGER
member_idTEXT
tierTEXT
amountREAL
Sample rows of card_spend
txn_idmember_idtieramount
1m1Gold100
2m2Gold200
3m3Gold300
4m4Gold400
5m5Gold500
6p1Platinum600
7p1Platinum400
8p2Platinum3000
Expected output on the sample data
tiermembersp90_spendmembers_at_or_above
Gold55001
Platinum330001

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‹ Structuring: Near-Threshold Deposits in 7 Days · Month-over-Month Credit Spikes ›

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